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Annotation of researchv10dc/vol2/pic/pic.cstr, revision 1.1

1.1     ! root        1: .so ../ADM/mac
        !             2: ....XX pic 53 "Pic \(em A Graphics Language for Typesetting"
        !             3: ...\" Wed Sep 24 15:49:34 EDT 1986
        !             4: .de IT
        !             5: \\$3\f2\\$1\f1\\$2
        !             6: ..
        !             7: .TR 116
        !             8: .ND "Revised, May, 1991
        !             9: .TL
        !            10: PIC \(em A Graphics Language for Typesetting
        !            11: .br
        !            12: User Manual\(dg
        !            13: .AU
        !            14: Brian W. Kernighan
        !            15: .AI
        !            16: .MH
        !            17: .AB
        !            18: .PP
        !            19: .IT Pic
        !            20: is a language for drawing simple figures
        !            21: on a typesetter.
        !            22: The basic objects in
        !            23: .IT pic
        !            24: are
        !            25: boxes,
        !            26: circles,
        !            27: ellipses,
        !            28: lines,
        !            29: arrows,
        !            30: arcs,
        !            31: spline curves,
        !            32: and text.
        !            33: These may be placed anywhere,
        !            34: at positions specified absolutely
        !            35: or in terms of previous objects.
        !            36: The example below illustrates the style and basic capabilities
        !            37: of the language.
        !            38: .PS
        !            39: ellipse "document"
        !            40: arrow
        !            41: box "PIC"
        !            42: arrow
        !            43: box "TBL/EQN" "(optional)" dashed
        !            44: arrow
        !            45: box "TROFF"
        !            46: arrow
        !            47: ellipse "typesetter"
        !            48: .PE
        !            49: This picture was created with the input
        !            50: .P1
        !            51:        \&.PS
        !            52:        ellipse "document"
        !            53:        arrow
        !            54:        box "PIC"
        !            55:        arrow
        !            56:        box "TBL/EQN" "(optional)" dashed
        !            57:        arrow
        !            58:        box "TROFF"
        !            59:        arrow
        !            60:        ellipse "typesetter"
        !            61:        \&.PE
        !            62: .P2
        !            63: .PP
        !            64: .IT Pic 
        !            65: is a
        !            66: .IT troff
        !            67: preprocessor;
        !            68: it passes most of its input through untouched, but translates
        !            69: commands between
        !            70: .CW .PS
        !            71: and
        !            72: .CW .PE
        !            73: into
        !            74: .IT troff
        !            75: commands that draw the pictures.
        !            76: .AE
        !            77: .FS
        !            78: \(dg This is a revised version of |reference(pic cstr 116).
        !            79: .FE
        !            80: .NH
        !            81: Introduction
        !            82: .PP
        !            83: .IT Pic
        !            84: is a language for drawing
        !            85: pictures.
        !            86: It operates as yet another
        !            87: .IT troff
        !            88: |reference(latest reference troff)
        !            89: preprocessor
        !            90: (in the same style as
        !            91: .IT eqn
        !            92: |reference(latest eqn) and
        !            93: .IT tbl
        !            94: |reference(latest tbl)),
        !            95: with pictures delimited by
        !            96: .CW .PS
        !            97: and
        !            98: .CW .PE .
        !            99: .PP
        !           100: .IT Pic
        !           101: was inspired partly by Chris Van Wyk's
        !           102: early work on
        !           103: .IT ideal
        !           104: |reference(ideal acm);
        !           105: it has somewhat the same capabilities,
        !           106: but quite a different flavor.
        !           107: In particular,
        !           108: .IT pic
        !           109: is much more procedural\(ema picture
        !           110: is drawn by specifying (sometimes in painful detail)
        !           111: the motions that one goes through to draw it.
        !           112: Other direct influences include the PICTURE language
        !           113: |reference(beatty picture),
        !           114: the V viewgraph language |reference(viewgraph-v),
        !           115: and, more recently, new features from the
        !           116: .IT grap
        !           117: language |reference(bentley kernighan grap)
        !           118: for typesetting graphs.
        !           119: .PP
        !           120: This paper is primarily a user's manual for
        !           121: .IT pic ;
        !           122: a discussion of design issues and user experience
        !           123: may be found in
        !           124: |reference(kernighan pic spe).
        !           125: The next section shows how to use
        !           126: .IT pic
        !           127: in the most simple way.
        !           128: Subsequent sections describe how to change
        !           129: the sizes of objects when the defaults are wrong,
        !           130: and how to change their positions when the standard positioning rules
        !           131: are wrong.
        !           132: An appendix describes the language succinctly and
        !           133: summarizes changes since the last manual.
        !           134: .........
        !           135: .NH
        !           136: Basics
        !           137: .PP
        !           138: .IT Pic
        !           139: provides boxes, lines, arrows, circles, ellipses, arcs,
        !           140: and splines (smooth curves),
        !           141: plus facilities for positioning
        !           142: and labeling them.
        !           143: The picture below shows all of the fundamental objects
        !           144: (except for splines)
        !           145: in their default sizes:
        !           146: .PS
        !           147: box "box"
        !           148: move
        !           149: line "line" above
        !           150: move
        !           151: arrow "arrow" above
        !           152: move
        !           153: circle "circle"
        !           154: move
        !           155: ellipse "ellipse"
        !           156: move down .25 right
        !           157: arc "arc"
        !           158: .PE
        !           159: Each picture begins with
        !           160: .CW .PS
        !           161: and ends with
        !           162: .CW .PE ;
        !           163: between them are commands to describe the picture.
        !           164: Each command is typed on a line by itself.
        !           165: For example
        !           166: .P1
        !           167: \&.PS
        !           168: box "this is" "a box"
        !           169: \&.PE
        !           170: .P2
        !           171: creates a standard box (\(34 inch wide, \(12 inch high)
        !           172: and centers the two pieces of text in it:
        !           173: .PS
        !           174: box "this is" "a box"
        !           175: .PE
        !           176: .PP
        !           177: Each line of text is a separate quoted string.
        !           178: Quotes are mandatory, even if the text contains no blanks.
        !           179: (Of course there needn't be any text at all.)
        !           180: Each line will be
        !           181: printed in the current size and font,
        !           182: centered horizontally, and separated
        !           183: vertically by the current
        !           184: .IT troff
        !           185: line spacing.
        !           186: .IT Pic
        !           187: does
        !           188: not
        !           189: center the complete drawing itself,
        !           190: but the default definitions of
        !           191: .CW .PS
        !           192: and
        !           193: .CW .PE
        !           194: in the
        !           195: .CW -ms
        !           196: macro package do.
        !           197: .PP
        !           198: You can use
        !           199: .CW circle
        !           200: or
        !           201: .CW ellipse
        !           202: in place of
        !           203: .CW box :
        !           204: .PS
        !           205: circle "this is" "a box"
        !           206: move; move
        !           207: ellipse "this is" "a box"
        !           208: .PE
        !           209: .PP
        !           210: Text is centered on lines and arrows; if there is more than one
        !           211: line of text, the lines are centered above and below:
        !           212: .P1
        !           213: line "this is" "a line"
        !           214: .P2
        !           215: .PS
        !           216: line "this is" "a line"
        !           217: .PE
        !           218: .P1
        !           219: arrow "this is" "an arrow"
        !           220: .P2
        !           221: .PS
        !           222: arrow "this is" "an arrow"
        !           223: .PE
        !           224: .PP
        !           225: Boxes and lines may be dashed or dotted;
        !           226: just add the word
        !           227: .CW dashed
        !           228: or
        !           229: .CW dotted
        !           230: after
        !           231: .CW box
        !           232: or
        !           233: .CW line :
        !           234: .P1
        !           235: line dashed "dashed" "line"
        !           236: .P2
        !           237: .PS
        !           238: line dashed "dashed" "line"
        !           239: .PE
        !           240: .PP
        !           241: Arcs by default turn 90 degrees counterclockwise from the current direction;
        !           242: you can make them turn clockwise by saying
        !           243: .CW arc
        !           244: .CW cw :
        !           245: .P1
        !           246: line; arc; arc cw; arrow
        !           247: .P2
        !           248: .PS
        !           249: line; arc; arc cw; arrow
        !           250: .PE
        !           251: A spline might well do this job better; we will return to that shortly.
        !           252: .PP
        !           253: As you might guess,
        !           254: .P1
        !           255: arc; arc; arc; arc
        !           256: .P2
        !           257: draws a circle, though not very efficiently.
        !           258: Notice that several commands can be put on a single line
        !           259: if they are separated by semicolons.
        !           260: .PP
        !           261: Objects are normally drawn one after another,
        !           262: left to right,
        !           263: and connected at the obvious places:
        !           264: .P1
        !           265: arrow; box "input"; arrow; box "process"; arrow; box "output"; arrow
        !           266: .P2
        !           267: .PS
        !           268: arrow; box "input"; arrow; box "process"; arrow; box "output"; arrow
        !           269: .PE
        !           270: One way to leave a space is with
        !           271: .CW move :
        !           272: .P1
        !           273: box; move; box; move; box
        !           274: .P2
        !           275: .PS
        !           276: box; move; box; move; box
        !           277: .PE
        !           278: .PP
        !           279: Although objects are normally connected left to right,
        !           280: this can be changed.
        !           281: If you specify a direction (as a separate object), subsequent objects
        !           282: will be joined in that direction:
        !           283: .P1
        !           284: down; box; arrow; ellipse; arrow; circle
        !           285: .P2
        !           286: .PS
        !           287: down; box; arrow; ellipse; arrow; circle
        !           288: .PE
        !           289: .P1
        !           290: left; box; arrow; ellipse; arrow; circle
        !           291: .P2
        !           292: .PS
        !           293: left; box; arrow; ellipse; arrow; circle
        !           294: .PE
        !           295: Each new picture begins going to the right.
        !           296: .PP
        !           297: Normally, figures are drawn at a fixed scale,
        !           298: with objects of a standard size.
        !           299: It is possible, however, to arrange that a figure be expanded or shrunk
        !           300: to fit a particular width.
        !           301: If the
        !           302: .CW .PS
        !           303: line contains a number, the drawing is forced to be that many inches wide,
        !           304: with the height scaled proportionately.
        !           305: Thus
        !           306: .P1
        !           307: \&.PS 3.5
        !           308: .P2
        !           309: causes the picture to be 3.5 inches wide.
        !           310: If two dimensions are specified, the second is the height.
        !           311: .PP
        !           312: .IT Pic
        !           313: is pretty dumb about the size of text in relation
        !           314: to the size of boxes, circles, and so on.
        !           315: There is no way to say
        !           316: ``make a box that just fits around this text''
        !           317: or ``make this text fit inside this circle''
        !           318: or ``draw a line as long as this text.''
        !           319: Tight fitting of text
        !           320: can generally only be done by trial and error.
        !           321: .PP
        !           322: Speaking of errors,
        !           323: if you make a grammatical error in the way you describe
        !           324: a picture,
        !           325: .IT pic
        !           326: will complain and try to indicate where.
        !           327: For example, the invalid input
        !           328: .P1
        !           329: box arrow box
        !           330: .P2
        !           331: will draw the message
        !           332: .P1
        !           333: pic: syntax error near line 5, file -
        !           334:  context is
        !           335:         box >>>  arrow <<<  box
        !           336: .P2
        !           337: The brackets
        !           338: point to the place where the error was first noted;
        !           339: it sometimes follows 
        !           340: the word in error, although in this example it's right on target.
        !           341: The filename
        !           342: .CW - ' `
        !           343: is the standard input.
        !           344: .NH
        !           345: Controlling Sizes
        !           346: .PP
        !           347: This section deals with how to
        !           348: control the sizes of objects
        !           349: when the default sizes are not what is wanted.
        !           350: The next section deals with positioning them
        !           351: when the default positions are not right.
        !           352: .PP
        !           353: Each object that
        !           354: .IT pic
        !           355: knows about
        !           356: (boxes, circles, etc.) has
        !           357: associated dimensions, like height, width, radius, and so on.
        !           358: By default,
        !           359: .IT pic
        !           360: tries to choose sensible default values for these dimensions,
        !           361: so that simple pictures can be drawn with a minimum
        !           362: of fuss and bother.
        !           363: All of the figures and motions shown so far
        !           364: have been in their default sizes:
        !           365: .DS
        !           366: .ta 1i
        !           367: box    \(34" wide \(mu \(12" high
        !           368: circle \(12" diameter
        !           369: ellipse        \(34" wide \(mu \(12" high
        !           370: arc    \(12" radius
        !           371: line or arrow  \(12" long
        !           372: move   \(12" in the current direction
        !           373: .DE
        !           374: .LP
        !           375: When necessary,
        !           376: you can make any object any size you want:
        !           377: .P1
        !           378: box width 3 height 0.1; circle radius 0.1
        !           379: .P2
        !           380: .PS
        !           381:        box wid 3 ht 0.1; circle radius 0.1
        !           382: .PE
        !           383: All positions and dimensions are in inches, so
        !           384: the box is 3 inches wide and 1/10 inch high and the circle has radius 1/10 inch.
        !           385: .PP
        !           386: An attribute like 
        !           387: .CW width
        !           388: changes only the one instance of the object.
        !           389: You can also change the default size for all objects
        !           390: of a particular type by assigning values to
        !           391: .IT pic
        !           392: variables;
        !           393: this will be discussed in Section 6.
        !           394: .PP
        !           395: The attributes of
        !           396: .CW height
        !           397: (which you can abbreviate to
        !           398: .CW ht )
        !           399: and
        !           400: .CW width
        !           401: (or
        !           402: .CW wid )
        !           403: apply to boxes, circles,
        !           404: ellipses,
        !           405: and to the head on an arrow.
        !           406: The attributes of
        !           407: .CW radius
        !           408: (or
        !           409: .CW rad )
        !           410: and
        !           411: .CW diameter
        !           412: (or
        !           413: .CW diam )
        !           414: can be used for circles and arcs if they seem more natural.
        !           415: .PP
        !           416: Lines and arrows are most easily drawn by specifying
        !           417: the amount of motion from where you are right now,
        !           418: in terms of directions.
        !           419: Accordingly the words
        !           420: .CW up ,
        !           421: .CW down ,
        !           422: .CW left
        !           423: and
        !           424: .CW right
        !           425: and an optional distance can be attached to
        !           426: .CW line ,
        !           427: .CW arrow ,
        !           428: and
        !           429: .CW move :
        !           430: .P1
        !           431: line up 1 right 2
        !           432: arrow left 2
        !           433: move left 0.1
        !           434: line <-> down 1 "height " rjust
        !           435: .P2
        !           436: .PS
        !           437: line up 1 right 2
        !           438: arrow left 2
        !           439: move left 0.1
        !           440: line <-> down 1 "height " rjust
        !           441: .PE
        !           442: The notation
        !           443: .CW <->
        !           444: indicates a two-headed arrow;
        !           445: use
        !           446: .CW ->
        !           447: for a head on the end and
        !           448: .CW <-
        !           449: for one on the start.
        !           450: Lines and arrows are really the same thing;
        !           451: in fact,
        !           452: .CW arrow
        !           453: is a synonym for
        !           454: .CW line
        !           455: .CW -> .
        !           456: .PP
        !           457: If you don't specify any distance after
        !           458: .CW up ,
        !           459: .CW down ,
        !           460: etc.,
        !           461: .IT pic
        !           462: uses the standard distance:
        !           463: .P1
        !           464: line up right; line down; line down left; line up
        !           465: .P2
        !           466: .PS
        !           467: line up right; line down; line down left; line up
        !           468: .PE
        !           469: If you omit the direction associated with a distance,
        !           470: the current direction is used.
        !           471: .PP
        !           472: Boxes and lines may be dotted or dashed:
        !           473: .P1
        !           474: box dotted; line dotted; move; line dashed; box dashed
        !           475: .P2
        !           476: .PS
        !           477: box dotted; line dotted; move; line dashed; box dashed
        !           478: .PE
        !           479: If there is a number after
        !           480: .CW dot ,
        !           481: the dots will be approximately that far apart.
        !           482: You can also control the size of the dashes (at least somewhat):
        !           483: if there is a length after the word
        !           484: .CW dashed ,
        !           485: the dashes will be that long,
        !           486: and the intervening spaces will be as close as possible to that size:
        !           487: .P1
        !           488: line right 5 dashed; move left 5 down .25; right
        !           489: line right 5 dashed 0.25; move left 5 down .25; right
        !           490: line right 5 dashed 0.5; move left 5 down .25; right
        !           491: line right 5 dashed 1
        !           492: .P2
        !           493: .PS
        !           494: line right 5 dashed; move left 5 down .25; right
        !           495: line right 5 dashed 0.25; move left 5 down .25; right
        !           496: line right 5 dashed 0.5; move left 5 down .25; right
        !           497: line right 5 dashed 1
        !           498: .PE
        !           499: Dotted or dashed attributes apply only to lines and boxes.
        !           500: .LP
        !           501: .PP
        !           502: You can make any object invisible by adding the word
        !           503: .CW invis
        !           504: after it.
        !           505: This is particularly useful for positioning things correctly
        !           506: near text:
        !           507: .P1
        !           508: box invis "input"; arrow; box invis "output"
        !           509: .P2
        !           510: .PS
        !           511: box invis "input"; arrow; box invis "output"
        !           512: .PE
        !           513: .PP
        !           514: Text may be positioned on lines and arrows:
        !           515: .P1
        !           516: arrow "on top of"; move
        !           517: arrow "above" "below"; move
        !           518: arrow "above" above; move
        !           519: arrow "below" below; move
        !           520: arrow "above" "on top of" "below"
        !           521: .P2
        !           522: .PS
        !           523: arrow "on top of"; move
        !           524: arrow "above" "below"; move
        !           525: arrow "above" above; move
        !           526: arrow "below" below; move
        !           527: arrow "above" "on top of" "below"
        !           528: .PE
        !           529: .LP
        !           530: .PP
        !           531: The ``width'' of an arrowhead is the distance across
        !           532: its tail;
        !           533: the ``height'' is the distance along the shaft.
        !           534: The arrowheads in this picture are default size and shape.
        !           535: .PP
        !           536: As we said earlier, arcs go 90 degrees counterclockwise
        !           537: from where you are right now, and
        !           538: .CW arc
        !           539: .CW cw
        !           540: changes this to clockwise.
        !           541: The default radius is the same as for circles,
        !           542: but you can change it with the
        !           543: .CW rad
        !           544: attribute.
        !           545: It is also easy to draw arcs between specific places;
        !           546: this will be described in the next section.
        !           547: .PP
        !           548: To put an arrowhead on an arc, use one of
        !           549: .CW <- ,
        !           550: .CW ->
        !           551: or
        !           552: .CW <-> ,
        !           553: as with lines.
        !           554: .LP
        !           555: .PP
        !           556: In all cases,
        !           557: unless an explicit dimension for some object is specified,
        !           558: you will get the default size.
        !           559: If you want an object to have the same size
        !           560: as the previous one of that kind,
        !           561: add the word
        !           562: .CW same .
        !           563: Thus
        !           564: in the set of boxes given by
        !           565: .P1
        !           566: down; box ht 0.2 wid 1.5; move down 0.15; box same; move same; box same
        !           567: .P2
        !           568: .PS
        !           569: down; box ht 0.2 wid 1.5; move down 0.15; box same; move same; box same
        !           570: .PE
        !           571: the dimensions set by the first
        !           572: .CW box
        !           573: are used several times;
        !           574: similarly, the amount of motion for the second
        !           575: .CW move
        !           576: is the same as for the first one.
        !           577: .PP
        !           578: You can change the default sizes of objects
        !           579: by assigning values to the variables that define their values.
        !           580: Here is the list, with their default values:
        !           581: .P1
        !           582: .ta 2i 3.3i
        !           583: boxwid = 0.75; boxht = 0.5
        !           584: linewid = 0.75;        lineht = 0.5
        !           585: circlerad = 0.25;      arcrad = 0.25
        !           586: ellipsewid = 0.75;     ellipseht = 0.5
        !           587: movewid = 0.75;        moveht = 0.5
        !           588: textwid = 0;   textht = 0
        !           589: arrowwid = 0.05;       arrowht = 0.1   \f1(These refer to the arrowhead.)\fP
        !           590: dashwid = 0.05;        arrowhead = 2   \f1(Arrowhead fill style)\fP
        !           591: maxpsht = 8.5; maxpswid = 11   \f1(Maximum picture dimensions)\fP
        !           592: fillval = 0.3; scale = 1
        !           593: .P2
        !           594: So if you want all your boxes to be long and skinny, and relatively close together,
        !           595: .P1
        !           596: boxwid = 0.1; boxht = 1
        !           597: movewid = 0.2
        !           598: box; move; box; move; box
        !           599: .P2
        !           600: .PS
        !           601: boxwid = 0.1; boxht = 1
        !           602: movewid = 0.2
        !           603: box; move; box; move; box
        !           604: .PE
        !           605: .nf
        !           606: .PS
        !           607: x = boxwid
        !           608:  y = boxht
        !           609: boxwid = 0.1
        !           610:  boxht = 1
        !           611: movewid = 0.2
        !           612: boxwid = x
        !           613:  boxht = y
        !           614: arrowhead = 7
        !           615:  arrowhead = 2
        !           616: .PE
        !           617: .PP
        !           618: Setting the variable
        !           619: .CW arrowhead
        !           620: to a value like 7 causes arrowheads to be filled by overstriking;
        !           621: the default is 2:
        !           622: .P1
        !           623: arrowhead = 7; arrow; move; arrowhead = 2; arrow
        !           624: .P2
        !           625: .PS
        !           626: arrowhead = 7; arrow; move; arrowhead = 2; arrow
        !           627: .PE
        !           628: .PP
        !           629: .IT Pic
        !           630: works internally in inches.
        !           631: Setting the variable
        !           632: .CW scale
        !           633: to some value causes all dimensions to be scaled down
        !           634: by that value.
        !           635: Thus, for example,
        !           636: .CW scale=2.54
        !           637: causes dimensions to be interpreted as centimeters.
        !           638: .PP
        !           639: The numbers given in the
        !           640: .CW .PS
        !           641: line override the dimensions given in the picture;
        !           642: these can be used to force a picture to a particular width and height.
        !           643: Experience indicates that a good way to get a picture
        !           644: of the right size is to enter its dimensions in inches,
        !           645: then if necessary add a width and perhaps height to the
        !           646: .CW .PS
        !           647: line.
        !           648: .PP
        !           649: Once set, variables like
        !           650: .CW boxht
        !           651: retain their values from one picture to the next.
        !           652: You can reset variables to their default values by listing them in a
        !           653: .CW reset
        !           654: statement:
        !           655: .P1
        !           656: reset boxht, boxwid
        !           657: .P2
        !           658: A bare
        !           659: .CW reset
        !           660: resets all variables.
        !           661: .PP
        !           662: There is a minimal facility for filling or shading objects,
        !           663: intended for Postscript output devices.
        !           664: The attribute
        !           665: .CW fill
        !           666: .IT expr
        !           667: sets the gray scale value to
        !           668: .IT expr ;
        !           669: the default, determined by the variable
        !           670: .CW fillval ,
        !           671: is 0.3.
        !           672: Following Postscript, smaller values are darker.
        !           673: Thus:
        !           674: .P1
        !           675: box fill
        !           676: box ht boxht/2 wid boxwid/2 "hello" at last box
        !           677: .P2
        !           678: .PS
        !           679: reset
        !           680: box fill
        !           681: box ht boxht/2 wid boxwid/2 "hello" at last box
        !           682: .PE
        !           683: .CW fill
        !           684: currently only applies to boxes, circles, and ellipses.
        !           685: .NH
        !           686: Controlling Positions
        !           687: .PP
        !           688: You can place things anywhere you want;
        !           689: .IT pic
        !           690: provides a variety of ways to talk about positions.
        !           691: .IT Pic
        !           692: uses a standard Cartesian coordinate system with
        !           693: .IT x
        !           694: increasing rightwards and
        !           695: .IT y
        !           696: increasing upwards,
        !           697: so any point or object has an
        !           698: .IT x
        !           699: and
        !           700: .IT y
        !           701: position, measured in inches.
        !           702: The first object is placed with its start at position 0,0 by default.
        !           703: The
        !           704: .IT x,y
        !           705: position of a box, circle or ellipse is its geometric center;
        !           706: the position of a line or spline or motion is its beginning;
        !           707: the position of an arc is the center of the corresponding circle.
        !           708: .PP
        !           709: Position modifiers like
        !           710: .CW from ,
        !           711: .CW to ,
        !           712: .CW by
        !           713: and
        !           714: .CW at
        !           715: are followed by an
        !           716: .IT x,y
        !           717: pair, and
        !           718: can be attached to boxes, circles, lines, motions, and so on,
        !           719: to specify or modify a position.
        !           720: .PP
        !           721: You can also use
        !           722: .CW up ,
        !           723: .CW down ,
        !           724: .CW right ,
        !           725: and
        !           726: .CW left
        !           727: with
        !           728: .CW line
        !           729: and
        !           730: .CW move :
        !           731: .P1
        !           732: box ht 0.2 wid 0.2 at 0,0 "1"
        !           733: move right 0.5                 # or "move to 0.5,0"
        !           734: box ht 0.2 wid 0.2 "2"
        !           735: move right 0.5                 # or "move 0.5" or "move same"
        !           736: box ht 0.2 wid 0.2 "3"
        !           737: .P2
        !           738: .PS 2
        !           739: box ht 0.2 wid 0.2 at 0,0 "1"
        !           740: move right 0.5                 # or "move to 0.5,0"
        !           741: box ht 0.2 wid 0.2 "2"
        !           742: move right 0.5
        !           743: box ht 0.2 wid 0.2 "3"
        !           744: .PE
        !           745: Comments can be used in pictures;
        !           746: they begin with a
        !           747: .CW #
        !           748: and end at the end of the line.
        !           749: .PP
        !           750: Attributes like
        !           751: .CW ht
        !           752: and
        !           753: .CW wid
        !           754: and positions like
        !           755: .CW at
        !           756: can be written out in any order.
        !           757: So
        !           758: .P1
        !           759: box ht 0.2 wid 0.2 at 0,0
        !           760: box at 0,0 wid 0.2 ht 0.2
        !           761: box ht 0.2 at 0,0 wid 0.2
        !           762: .P2
        !           763: are all equivalent, though the last is harder to read
        !           764: and thus less desirable.
        !           765: .PP
        !           766: The
        !           767: .CW from
        !           768: and
        !           769: .CW to
        !           770: attributes are particularly useful with arcs,
        !           771: to specify the endpoints.
        !           772: By default, arcs are drawn counterclockwise,
        !           773: .P1
        !           774: "+" at 0,0
        !           775: arc -> from 0.5,0 to 0,0.5
        !           776: arc -> cw from 0,0 to 1,0.5
        !           777: .P2
        !           778: .PS
        !           779: "+" at 0,0
        !           780: arc -> from 0.5,0 to 0,0.5
        !           781: arc -> cw from 0,0 to 1,0.5
        !           782: .PE
        !           783: The radius can be made large to provide flat arcs:
        !           784: .P1
        !           785: arc -> cw from 0,0 to 2,0 rad 15
        !           786: .P2
        !           787: .PS
        !           788: arc -> cw from 0,0 to 2,0 rad 15
        !           789: .PE
        !           790: If the circle is under-specified,
        !           791: .IT pic
        !           792: guesses a radius and/or center;
        !           793: you will have to provide them explicitly if the guess is wrong.
        !           794: .LP
        !           795: .PP
        !           796: We said earlier that
        !           797: objects are normally connected left to right.
        !           798: This is an over-simplification.
        !           799: The truth is that objects are connected together
        !           800: in the direction specified by the most recent
        !           801: .CW up ,
        !           802: .CW down ,
        !           803: .CW left
        !           804: or
        !           805: .CW right
        !           806: (either alone or as part of some object).
        !           807: Thus, in
        !           808: .P1
        !           809: arrow left; box; arrow; circle; arrow
        !           810: .P2
        !           811: the
        !           812: .CW left
        !           813: implies connection towards the left:
        !           814: .PS
        !           815: arrow left; box; arrow; circle; arrow
        !           816: .PE
        !           817: This could also be written as
        !           818: .P1
        !           819: left; arrow; box; arrow; circle; arrow
        !           820: .P2
        !           821: .PP
        !           822: Objects are joined in the direction determined by the last
        !           823: .CW up ,
        !           824: .CW down ,
        !           825: etc., with the entry point of the second object attached
        !           826: to the exit point of the first
        !           827: (which is fixed at the time of entry).
        !           828: Entry and exit points for boxes, circles and ellipses are
        !           829: on opposite sides.
        !           830: This automatic connection and direction selection
        !           831: works well if the direction doesn't change but it will occasionally surprise you:
        !           832: .P1
        !           833: arrow; circle; down; arrow
        !           834: .P2
        !           835: .PS
        !           836: arrow; circle; down; arrow
        !           837: .PE
        !           838: The arrow comes out of the right side of the circle, not the bottom,
        !           839: as might be expected.
        !           840: .PP
        !           841: If a set of commands is enclosed in braces
        !           842: .CW {...} ,
        !           843: the current position and direction of motion when the group is finished
        !           844: will be exactly where it was when entered.
        !           845: Nothing else is restored.
        !           846: There is also a more general way to group objects,
        !           847: using
        !           848: .CW [
        !           849: and
        !           850: .CW ] ,
        !           851: which is discussed in Section 9.
        !           852: .NH
        !           853: Labels and Corners
        !           854: .PP
        !           855: Objects can be labelled or named so that you can talk about them later.
        !           856: For example,
        !           857: .P1
        !           858: Box1:  box
        !           859:        # ... other stuff ...
        !           860:        move to Box1
        !           861: .P2
        !           862: Place names 
        !           863: .IT must
        !           864: begin with an upper case letter
        !           865: (to distinguish them from variable names,
        !           866: which begin with lower case letters).
        !           867: The name refers to the ``center''
        !           868: of the object,
        !           869: which is the geometric center for most things.
        !           870: .PP
        !           871: Other combinations also work:
        !           872: .P1
        !           873: line from Box1 to Box2
        !           874: move to Box1 up 0.1 right 0.2
        !           875: move to Box1 + 0.2,0.1 # same as previous
        !           876: line to Box1 - 0.5,0
        !           877: .P2
        !           878: The reserved name
        !           879: .CW Here
        !           880: may be used to refer to the current position.
        !           881: .PP
        !           882: Labels can be reset several times in a single picture,
        !           883: so a statement like
        !           884: .P1
        !           885: Box1:  Box1 + 1,1
        !           886: .P2
        !           887: is perfectly legal.
        !           888: .LP
        !           889: .PP
        !           890: You can also refer to previously drawn objects of each type,
        !           891: using the word
        !           892: .CW last .
        !           893: For example, given the input
        !           894: .P1
        !           895: box "A"; circle "B"; box "C"
        !           896: .P2
        !           897: then
        !           898: .CW last \& `
        !           899: .CW box '
        !           900: refers to box
        !           901: .CW C ,
        !           902: .CW last \& `
        !           903: .CW circle '
        !           904: refers to circle
        !           905: .CW B ,
        !           906: and
        !           907: .CW 2nd \& `
        !           908: .CW last
        !           909: .CW box '
        !           910: refers to box
        !           911: .CW A .
        !           912: Numbering of objects can also be done from the beginning,
        !           913: so boxes
        !           914: .CW A
        !           915: and
        !           916: .CW C
        !           917: are
        !           918: .CW 1st \& `
        !           919: .CW box '
        !           920: and
        !           921: .CW 2nd \& `
        !           922: .CW box '
        !           923: respectively.
        !           924: .PP
        !           925: To cut down the need for explicit coordinates,
        !           926: objects have ``corners'' named by compass points:
        !           927: .P1
        !           928: B: box "B.c" ht 1 wid 1.5
        !           929:        " B.e" at B.e ljust
        !           930:        " B.ne" at B.ne ljust
        !           931:        " B.se" at B.se ljust
        !           932:        "B.s" at B.s below
        !           933:        "B.n" at B.n above
        !           934:        "B.sw " at B.sw rjust
        !           935:        "B.w " at B.w rjust
        !           936:        "B.nw " at B.nw rjust
        !           937: .P2
        !           938: .PS
        !           939: B: box "B.c" ht 1 wid 1.5
        !           940: " B.e" at B.e ljust
        !           941: " B.ne" at B.ne ljust
        !           942: " B.se" at B.se ljust
        !           943: "B.s" at B.s below
        !           944: "B.n" at B.n above
        !           945: "B.sw " at B.sw rjust
        !           946: "B.w " at B.w rjust
        !           947: "B.nw " at B.nw rjust
        !           948: .PE
        !           949: Note the use of
        !           950: .CW ljust ,
        !           951: .CW rjust ,
        !           952: .CW above ,
        !           953: and
        !           954: .CW below
        !           955: to alter the default positioning of text,
        !           956: and of a blank within some strings to help space them away from a vertical line.
        !           957: .PP
        !           958: Lines and arrows have a
        !           959: .CW start ,
        !           960: an
        !           961: .CW end
        !           962: and a 
        !           963: .CW center
        !           964: in addition to corners.
        !           965: Circles and ellipses have corners too;
        !           966: an arc has the same corners as the circle of which it is a part.
        !           967: The words
        !           968: .CW left ,
        !           969: .CW right ,
        !           970: .CW top ,
        !           971: and
        !           972: .CW bottom
        !           973: are synonyms for
        !           974: .CW west ,
        !           975: .CW east ,
        !           976: .CW north
        !           977: and
        !           978: .CW south .
        !           979: .PP
        !           980: It is often easiest to position objects by positioning
        !           981: some part of one at some part of another,
        !           982: for example the southwest corner of one at the southeast corner
        !           983: of another.
        !           984: The
        !           985: .CW with
        !           986: attribute
        !           987: permits this kind of positioning:
        !           988: .P1
        !           989: box ht 0.75 wid 0.75
        !           990: box ht 0.5 wid 0.5 with .sw at last box.se
        !           991: .P2
        !           992: .PS
        !           993: box ht 0.75 wid 0.75
        !           994: box ht 0.5 wid 0.5 with .sw at last box.se
        !           995: .PE
        !           996: Notice that the corner after
        !           997: .CW with
        !           998: is written
        !           999: .CW .sw .
        !          1000: .PP
        !          1001: As another example, consider
        !          1002: .P1
        !          1003: ellipse
        !          1004: ellipse ht .2 wid .3 with .se at 1st ellipse.nw
        !          1005: ellipse ht .2 wid .3 with .sw at 1st ellipse.ne
        !          1006: .P2
        !          1007: .PS
        !          1008: ellipse
        !          1009: ellipse ht .2 wid .3 with .se at 1st ellipse.nw
        !          1010: ellipse ht .2 wid .3 with .sw at 1st ellipse.ne
        !          1011: .PE
        !          1012: .LP
        !          1013: .PP
        !          1014: Sometimes it is desirable to have a line intersect a circle
        !          1015: at a point which is not one of the eight compass points
        !          1016: that
        !          1017: .IT pic
        !          1018: knows about.
        !          1019: In such cases, the proper visual effect can be obtained by using
        !          1020: the attribute
        !          1021: .CW chop
        !          1022: to chop off part of the line:
        !          1023: .P1
        !          1024: circlerad = 0.15; arrowhead = 7
        !          1025: circle "a"
        !          1026: circle "b" at 1st circle - (0.4, 0.6)
        !          1027: circle "c" at 1st circle + (0.4, -0.6)
        !          1028: arrow from 1st circle to 2nd circle chop
        !          1029: arrow from 1st circle to 3rd circle chop
        !          1030: .P2
        !          1031: .PS
        !          1032: circlerad = 0.15; arrowhead = 7
        !          1033: circle "a"
        !          1034: circle "b" at 1st circle - (0.4, 0.6)
        !          1035: circle "c" at 1st circle + (0.4, -0.6)
        !          1036: arrow from 1st circle to 2nd circle chop
        !          1037: arrow from 1st circle to 3rd circle chop
        !          1038: reset
        !          1039: .PE
        !          1040: By default the line is chopped by
        !          1041: .CW circlerad
        !          1042: at each end.
        !          1043: This may be changed:
        !          1044: .P1
        !          1045: line ... chop \f2r\fP
        !          1046: .P2
        !          1047: chops both ends by
        !          1048: \f2r\fP, and
        !          1049: .P1
        !          1050: line ... chop \f2r1\fP chop \f2r2\fP
        !          1051: .P2
        !          1052: chops the beginning by
        !          1053: .IT r1
        !          1054: and the end by
        !          1055: .IT r2 .
        !          1056: More complicated intersections can be computed with
        !          1057: the built-in trigonometric functions listed in the next section.
        !          1058: .PP
        !          1059: There is one other form of positioning that is sometimes useful,
        !          1060: to refer to a point some fraction of the way between
        !          1061: two other points.
        !          1062: This can be expressed in 
        !          1063: .IT pic
        !          1064: as
        !          1065: .P1
        !          1066: \f2fraction\fP of the way between \f2position1\fP and \f2position2\fP
        !          1067: .P2
        !          1068: where
        !          1069: .IT fraction
        !          1070: is any expression, and
        !          1071: .IT position1
        !          1072: and
        !          1073: .IT position2
        !          1074: are any positions.
        !          1075: You can abbreviate this rather windy phrase;
        !          1076: ``of the way'' is optional, and the whole thing can
        !          1077: be written instead as
        !          1078: .P1
        !          1079: \f2fraction\fP < \f2position1\fP , \f2position2\fP >
        !          1080: .P2
        !          1081: As a pair of examples:
        !          1082: .P1
        !          1083: box
        !          1084: arrow right from 1/3 of the way between last box.ne and last box.se
        !          1085: arrow right from 2/3 <last box.ne, last box.se>
        !          1086: .P2
        !          1087: .PS
        !          1088: box
        !          1089: arrow right from 1/3 of the way between last box.ne and last box.se
        !          1090: arrow right from 2/3 <last box.ne, last box.se>
        !          1091: .PE
        !          1092: .P1
        !          1093: A:  ellipse
        !          1094:     ellipse ht .2 wid .3 with .se at 1st ellipse.nw
        !          1095:     ellipse ht .2 wid .3 with .sw at 1st ellipse.ne
        !          1096:     circle rad .05 at 0.5 <A.nw,A.c>
        !          1097:     circle rad .05 at 0.5 <A.ne,A.c>
        !          1098:     arc from 0.25 <A.w,A.e> to 0.75 <A.w,A.e>
        !          1099: .P2
        !          1100: .PS
        !          1101: A:     ellipse
        !          1102:        ellipse ht .2 wid .3 with .se at 1st ellipse.nw
        !          1103:        ellipse ht .2 wid .3 with .sw at 1st ellipse.ne
        !          1104:        circle rad .05 at 0.5 <A.nw,A.c>
        !          1105:        circle rad .05 at 0.5 <A.ne,A.c>
        !          1106:        arc from 0.25 <A.w,A.e> to 0.75 <A.w,A.e>
        !          1107: .PE
        !          1108: Naturally,
        !          1109: the distance given by
        !          1110: .IT fraction
        !          1111: can be greater than 1 or less than 0.
        !          1112: .PP
        !          1113: Advice:\ 
        !          1114: experience suggests that the easiest way to position objects
        !          1115: is by placing them relative to previous objects
        !          1116: and places, using
        !          1117: .CW with ,
        !          1118: .CW at ,
        !          1119: etc.
        !          1120: This is better than using
        !          1121: .CW move ;
        !          1122: you should generally avoid
        !          1123: .CW move .
        !          1124: .NH
        !          1125: Variables, Expressions and Built-in Functions
        !          1126: .PP
        !          1127: It's generally a bad idea to write everything in 
        !          1128: absolute coordinates if you are likely
        !          1129: to change things.
        !          1130: .IT Pic
        !          1131: variables let you parameterize your picture:
        !          1132: .P1
        !          1133: a = 0.5;  b = 1
        !          1134: 
        !          1135: box wid a ht b
        !          1136: ellipse wid a/2 ht 1.5*b
        !          1137: Box2:  Box1 - (a/2, b/2)
        !          1138: .P2
        !          1139: Expressions may use the standard operators
        !          1140: .CW + ,
        !          1141: .CW - ,
        !          1142: .CW * ,
        !          1143: .CW / ,
        !          1144: .CW % ,
        !          1145: .CW ^
        !          1146: (exponentiation),
        !          1147: and parentheses for grouping.
        !          1148: .PP
        !          1149: The most important variables are the predefined ones for
        !          1150: controlling the default sizes of objects,
        !          1151: listed in Section 3.
        !          1152: These may be set at any time in any picture,
        !          1153: and retain their values from picture to picture until reset.
        !          1154: .PP
        !          1155: You can use the height, width, radius,
        !          1156: and
        !          1157: .IT x
        !          1158: and
        !          1159: .IT y
        !          1160: coordinates of any object or corner in an expression:
        !          1161: .P1
        !          1162: Box1.x         # the \f2x\fP coordinate of the center of Box1
        !          1163: Box1.ne.y      # the \f2y\fP coordinate of the northeast corner of Box1
        !          1164: Box1.wid       # the width of Box1
        !          1165: Box1.ht                # and its height
        !          1166: 2nd last circle.rad    # the radius of the 2nd last circle
        !          1167: .P2
        !          1168: .PP
        !          1169: Any pair of expressions enclosed in parentheses
        !          1170: defines a position;  furthermore such positions
        !          1171: can be added or subtracted to yield new positions:
        !          1172: .EQ
        !          1173: delim $$
        !          1174: define cw X font CW X
        !          1175: .EN
        !          1176: .P1
        !          1177: (\f2x\fP, \f2y\fP)
        !          1178: ($x sub 1$, $y sub 1$) + ($x sub 2$, $y sub 2$)
        !          1179: .P2
        !          1180: If $p sub 1$ and $p sub 2$ are positions, then
        !          1181: $( p sub 1 , p sub 2 )$
        !          1182: refers to the point
        !          1183: $( p sub 1 font CW .x ,~ p sub 2 font CW .y )$.
        !          1184: .PP
        !          1185: .IT Pic
        !          1186: provides a small collection of standard functions:
        !          1187: .DS
        !          1188: .ta 3i
        !          1189: $cw "sin" (expr)$, $cw "cos" (expr)$, $cw atan2 (y,x)$ (angle in radians)
        !          1190: $cw "log" (expr)$, $cw "exp" (expr)$   (Beware: both base 10)
        !          1191: $cw "sqrt" (expr)$, $cw "max" (e sub 1 , e sub 2 )$, $cw "min" (e sub 1 , e sub 2 )$
        !          1192: $cw "int" (expr)$      (integer part of $expr$)
        !          1193: $cw rand ()$   (random number between 0 and 1)
        !          1194: .DE
        !          1195: .EQ
        !          1196: delim off
        !          1197: .EN
        !          1198: .NH
        !          1199: More on Text
        !          1200: .PP
        !          1201: Normally, text is centered
        !          1202: at the geometric center of the object it is associated with.
        !          1203: The attribute
        !          1204: .CW ljust
        !          1205: causes the left end to be at the specified point
        !          1206: (which means that the text lies to the right of the specified place!),
        !          1207: and
        !          1208: .CW rjust
        !          1209: puts the right end at the place.
        !          1210: .CW above
        !          1211: and
        !          1212: .CW below
        !          1213: center the text one half line space in the given direction.
        !          1214: .PP
        !          1215: Text attributes can be compounded:
        !          1216: .P1
        !          1217: arrow 1 "ljust above" ljust above
        !          1218: .P2
        !          1219: .PS
        !          1220: arrow 1 "ljust above" ljust above
        !          1221: .PE
        !          1222: .LP
        !          1223: .PP
        !          1224: Text is most often an attribute of some other object,
        !          1225: but you can also have self-standing text:
        !          1226: .P1
        !          1227: "origin" "(0,0)" at 0,0
        !          1228: "this is" "(1,1)" at 1,1
        !          1229: box ht 1 wid 1 dotted with .sw at 0,0
        !          1230: .P2
        !          1231: .PS
        !          1232: "origin" "(0,0)" at 0,0
        !          1233: "this is" "(1,1)" at 1,1
        !          1234: box ht 1 wid 1 dotted with .sw at 0,0
        !          1235: .PE
        !          1236: .LP
        !          1237: In effect, \f2n\fP text strings are contained in an invisible box
        !          1238: of width
        !          1239: .CW textwid
        !          1240: and height \f2n\fP \(mu
        !          1241: .CW textht .
        !          1242: The variables
        !          1243: .CW textwid
        !          1244: and
        !          1245: .CW textht
        !          1246: may be set to any values;
        !          1247: they are normally zero.
        !          1248: .PP
        !          1249: A list of numeric expressions can be converted to a formatted string
        !          1250: with the
        !          1251: .CW sprintf
        !          1252: function and used anywhere a quoted string can be:
        !          1253: .P1
        !          1254: B: box wid log(20)
        !          1255:    sprintf("width = %g, height = %g ", B.wid, B.ht) rjust at B.w
        !          1256: .P2
        !          1257: .PS
        !          1258: B: box wid log(20)
        !          1259:    sprintf("width = %g, height = %g ", B.wid, B.ht) rjust at B.w
        !          1260: .PE
        !          1261: .......
        !          1262: .NH
        !          1263: Lines and Splines
        !          1264: .PP
        !          1265: A ``line'' may actually be a path,
        !          1266: that is, it may consist of connected segments:
        !          1267: .P1
        !          1268: line right 1 then down .5 left 1 then right 1
        !          1269: .P2
        !          1270: .PS
        !          1271: line right 1 then down .5 left 1 then right 1
        !          1272: .PE
        !          1273: The word
        !          1274: .CW then
        !          1275: separates components of the path.
        !          1276: .PP
        !          1277: A spline is a smooth curve guided by a set of straight lines
        !          1278: just like the line above.
        !          1279: It begins at the same place, ends at the same place,
        !          1280: and in between is tangent to the mid-point of each guiding line.
        !          1281: The syntax for a spline is identical to a (path) line
        !          1282: except for using
        !          1283: .CW spline
        !          1284: instead of
        !          1285: .CW line :
        !          1286: .P1
        !          1287: line dashed right 1 then down .5 left 1 then right 1
        !          1288: spline from start of last line \e
        !          1289:   right 1 then down .5 left 1 then right 1
        !          1290: .P2
        !          1291: .PS
        !          1292: line dashed right 1 then down .5 left 1 then right 1
        !          1293: spline from start of last line \
        !          1294:   right 1 then down .5 left 1 then right 1
        !          1295: .PE
        !          1296: (Long input lines can be split by ending each piece
        !          1297: with a backslash.)
        !          1298: .PP
        !          1299: The elements of a path, whether line or spline,
        !          1300: are specified as a series of points,
        !          1301: either in absolute terms or by
        !          1302: .CW up ,
        !          1303: .CW down , 
        !          1304: etc.
        !          1305: .P1
        !          1306: spline right then up then left then down ->
        !          1307: .P2
        !          1308: .PS
        !          1309: spline right then up then left then down ->
        !          1310: .PE
        !          1311: .P1
        !          1312: spline right then up left then down ->
        !          1313: .P2
        !          1314: .PS
        !          1315: spline right then up left then down ->
        !          1316: .PE
        !          1317: .PP
        !          1318: Notice that arrowheads may be put on the ends
        !          1319: of a line or spline.
        !          1320: .NH
        !          1321: Blocks
        !          1322: .PP
        !          1323: Any sequence of
        !          1324: .IT pic
        !          1325: statements may be enclosed in
        !          1326: brackets
        !          1327: .CW [
        !          1328: and
        !          1329: .CW ]
        !          1330: to form
        !          1331: a block,
        !          1332: which can then be treated as a single object,
        !          1333: and manipulated rather like an ordinary box:
        !          1334: .P1
        !          1335: box "1"
        !          1336: [ box "2"; arrow "3" above; box "4" ] with .n at last box.s - (0,0.1)
        !          1337: "Thing 2: " rjust at last [].w
        !          1338: .P2
        !          1339: .PS
        !          1340: box "1"
        !          1341: [ box "2"; arrow "3" above; box "4" ] with .n at last box.s - (0,0.1)
        !          1342: "Thing 2: " rjust at last [].w
        !          1343: .PE
        !          1344: Notice that
        !          1345: ``last''-type constructs treat blocks as a unit and don't look
        !          1346: inside for objects:
        !          1347: .CW last "" ``
        !          1348: .CW box.s ''
        !          1349: refers to box 1, not box 2 or 4.
        !          1350: You can use
        !          1351: .CW last\ [] ,
        !          1352: etc.,
        !          1353: just like
        !          1354: .CW last\ box .
        !          1355: .PP
        !          1356: Blocks have the same compass corners as
        !          1357: boxes (determined by the bounding box).
        !          1358: It is also
        !          1359: possible to position a block by placing either an absolute 
        !          1360: coordinate (like
        !          1361: .CW 0,0 )
        !          1362: or an internal label (like
        !          1363: .CW A )
        !          1364: at some
        !          1365: external point, as in
        !          1366: .P1
        !          1367: [ ...; A: ...; ... ] with .A at ...
        !          1368: .P2
        !          1369: By default, blocks join with other things as boxes do, at the
        !          1370: center of the appropriate side.
        !          1371: .PP
        !          1372: Names of variables and places within a block are local
        !          1373: to that block, and thus do not affect variables and places
        !          1374: of the same name outside.
        !          1375: (In particular, that includes the built-in variables like
        !          1376: .CW boxwid ,
        !          1377: etc.;
        !          1378: if they are set within a block,
        !          1379: they revert to their original values when the block is left.)
        !          1380: You can get at the internal
        !          1381: place names with constructs like
        !          1382: .P1
        !          1383: last [].A
        !          1384: .P2
        !          1385: or
        !          1386: .P1
        !          1387: B.A
        !          1388: .P2
        !          1389: where
        !          1390: .CW B
        !          1391: is a name attached to a block:
        !          1392: .P1
        !          1393: B:  [ ... ;  A: ...;  ]
        !          1394: .P2
        !          1395: When combined with
        !          1396: .CW define
        !          1397: statements (next section), blocks provide
        !          1398: a reasonable simulation of a procedure mechanism.
        !          1399: .PP
        !          1400: Although blocks nest,
        !          1401: it is currently possible to look only one level deep
        !          1402: with constructs like
        !          1403: .CW B.A ,
        !          1404: although
        !          1405: .CW A
        !          1406: may be
        !          1407: further qualified by a corner name (i.e.,
        !          1408: .CW B.A.sw
        !          1409: or
        !          1410: .CW top
        !          1411: .CW of
        !          1412: .CW B.A
        !          1413: are legal).
        !          1414: .PP
        !          1415: The following example illustrates most of the points made above
        !          1416: about how blocks work:
        !          1417: .P1
        !          1418: h = .5;  dh = .02;  dw = .1
        !          1419: [
        !          1420:        Ptr: [
        !          1421:                boxht = h; boxwid = dw
        !          1422:                A: box
        !          1423:                B: box
        !          1424:                C: box
        !          1425:                box wid 2*boxwid "..."
        !          1426:                D: box
        !          1427:        ]
        !          1428:        Block: [
        !          1429:                boxht = 2*dw; boxwid = 2*dw
        !          1430:                movewid = 2*dh
        !          1431:                A: box; move
        !          1432:                B: box; move
        !          1433:                C: box; move
        !          1434:                box invis "..." wid 2*boxwid; move
        !          1435:                D: box
        !          1436:        ] with .t at Ptr.s - (0,h/2)
        !          1437:        arrow from Ptr.A to Block.A.nw + (dh,0)
        !          1438:        arrow from Ptr.B to Block.B.nw + (dh,0)
        !          1439:        arrow from Ptr.C to Block.C.nw + (dh,0)
        !          1440:        arrow from Ptr.D to Block.D.nw + (dh,0)
        !          1441: ]
        !          1442: box dashed ht last [].ht+dw wid last [].wid+dw at last []
        !          1443: .P2
        !          1444: This produces
        !          1445: .PS
        !          1446: h = .5
        !          1447: dh = .02
        !          1448: dw = .1
        !          1449: [
        !          1450:        Ptr: [
        !          1451:                boxht = h; boxwid = dw
        !          1452:                A: box
        !          1453:                B: box
        !          1454:                C: box
        !          1455:                box wid 2*boxwid "..."
        !          1456:                D: box
        !          1457:        ]
        !          1458:        Block: [
        !          1459:                boxht = 2*dw; boxwid = 2*dw
        !          1460:                movewid = 2*dh
        !          1461:                A: box; move
        !          1462:                B: box; move
        !          1463:                C: box; move
        !          1464:                box invis "..." wid 2*boxwid; move
        !          1465:                D: box
        !          1466:        ] with .t at Ptr.s - (0,h/2)
        !          1467:        arrow from Ptr.A to Block.A.nw + (dh,0)
        !          1468:        arrow from Ptr.B to Block.B.nw + (dh,0)
        !          1469:        arrow from Ptr.C to Block.C.nw + (dh,0)
        !          1470:        arrow from Ptr.D to Block.D.nw + (dh,0)
        !          1471: ]
        !          1472: box dashed ht last [].ht+dw wid last [].wid+dw at last []
        !          1473: .PE
        !          1474: .NH
        !          1475: Macros
        !          1476: .PP
        !          1477: .IT Pic
        !          1478: provides a basic macro facility.
        !          1479: In the simplest form,
        !          1480: .P1
        !          1481: define  \f2name\fP  { \f2replacement text\fP }
        !          1482: .P2
        !          1483: defines
        !          1484: .IT name
        !          1485: to be the
        !          1486: .IT "replacement text" .
        !          1487: Any subsequent occurrence of
        !          1488: .IT name
        !          1489: will be replaced by
        !          1490: .IT "replacement text" .
        !          1491: .PP
        !          1492: Macros may have arguments.
        !          1493: If the replacement text of a macro definition contains occurrences of
        !          1494: .CW $1 ,
        !          1495: .CW $2 ,
        !          1496: etc.,
        !          1497: these will be replaced by the corresponding actual arguments
        !          1498: when the macro is invoked.
        !          1499: The invocation for a macro with arguments is
        !          1500: .P1
        !          1501: name(arg1, arg2, ...)
        !          1502: .P2
        !          1503: Non-existent arguments are replaced by null strings.
        !          1504: Macro definitions last from picture to picture;
        !          1505: a macro definition can be removed by
        !          1506: .P1
        !          1507: undef \f2macro-name\fP
        !          1508: .P2
        !          1509: .PP
        !          1510: As an example, one might define a
        !          1511: .CW square
        !          1512: by
        !          1513: .P1
        !          1514: define square { box ht $1 wid $1  $2 }
        !          1515: .P2
        !          1516: and use it as
        !          1517: .P1
        !          1518: square(1, "one" "inch")
        !          1519: square(0.5)
        !          1520: square(0.25, "\es-4tiny\es+4" dashed)
        !          1521: .P2
        !          1522: .PS
        !          1523: define square { box ht $1 wid $1  $2 }
        !          1524: square(1, "one" "inch")
        !          1525: square(0.5)
        !          1526: square(0.25, "\s-4tiny\s+4" dashed)
        !          1527: .PE
        !          1528: Notice how the second argument may be used to pass in arbitrary contents.
        !          1529: .PP
        !          1530: Coordinates like
        !          1531: .IT x,y
        !          1532: may be enclosed in parentheses,
        !          1533: as in
        !          1534: .IT x,y ), (
        !          1535: so they can be included in a macro argument.
        !          1536: .NH
        !          1537: File Copy
        !          1538: .PP
        !          1539: The statement
        !          1540: .P1
        !          1541: copy "\f2filename\fP"
        !          1542: .P2
        !          1543: inserts the contents of the named file
        !          1544: at that point in the input.
        !          1545: Any
        !          1546: .CW .PS
        !          1547: or
        !          1548: .CW .PE
        !          1549: lines within the file
        !          1550: are ignored, so previously prepared pictures
        !          1551: can be used as parts of larger ones without editing.
        !          1552: .PP
        !          1553: .IT Pic
        !          1554: also provides the
        !          1555: .CW copy
        !          1556: .CW thru
        !          1557: mechanism found in
        !          1558: .IT grap :
        !          1559: .P1
        !          1560: copy "\f2file\fP" thru \f2macro-name\fP
        !          1561: .P2
        !          1562: copies
        !          1563: .IT file ,
        !          1564: treating each line as an invocation of the named macro
        !          1565: (each field being an argument).
        !          1566: A literal macro may be used instead of a name:
        !          1567: .P1
        !          1568: copy "\f2file\fP" thru { \f2macro replacement text\fP }
        !          1569: .P2
        !          1570: and if no file name is given,
        !          1571: the remainder of the input until the next
        !          1572: .CW .PE
        !          1573: is used.
        !          1574: So to plot a set of circles at points whose coordinates and radii
        !          1575: are included in-line:
        !          1576: .P1
        !          1577: copy thru { circle rad $3 at $1,$2 }
        !          1578: 0 0 .05
        !          1579: 1 1 .1
        !          1580: .2 .3 .03
        !          1581: .4 .7 .05
        !          1582: \&...
        !          1583: .P2
        !          1584: .PS
        !          1585: copy thru { circle rad $3 at $1,$2 }
        !          1586: 0 0 .05
        !          1587: 1 1 .1
        !          1588: .2 .3 .03
        !          1589: .4 .7 .05
        !          1590: .1 .8 .1
        !          1591: .4 .9 .02
        !          1592: .7 .5 .15
        !          1593: 1 .4 .04
        !          1594: .8 0 .075
        !          1595: .5 .25 .03
        !          1596: .PE
        !          1597: .PP
        !          1598: The
        !          1599: .CW sh
        !          1600: command executes an arbitrary commandline:
        !          1601: .P1
        !          1602: sh { \f2anything\fP }
        !          1603: .P2
        !          1604: Macros within
        !          1605: .IT anything
        !          1606: are expanded first.
        !          1607: .NH
        !          1608: Loops and Conditionals
        !          1609: .PP
        !          1610: .IT Pic
        !          1611: provides an
        !          1612: .CW if
        !          1613: statement and a
        !          1614: .CW for
        !          1615: loop.
        !          1616: .P1
        !          1617: pi = atan2(0,-1)
        !          1618: for i = 0 to 2 * pi by 0.1 do {
        !          1619:        "\-" at i/2, 0
        !          1620:        "s" at i/2, sin(i)/2
        !          1621:        "c" at i/2, cos(i)/2
        !          1622: }
        !          1623: .P2
        !          1624: .PS
        !          1625: .ps -2
        !          1626: pi = atan2(0,-1)
        !          1627: for i = 0 to 2 * pi by 0.1 do {
        !          1628:        "\-" at i/2, 0
        !          1629:        "s" at i/2, sin(i)/2
        !          1630:        "c" at i/2, cos(i)/2
        !          1631: }
        !          1632: .ps +2
        !          1633: .PE
        !          1634: The
        !          1635: .CW by
        !          1636: clause is optional;
        !          1637: if the value is preceded by a
        !          1638: .CW * ,
        !          1639: the steps are multiplicative, not additive.
        !          1640: The body of the loop is delimited by braces,
        !          1641: which are also used for definitions,
        !          1642: .CW copy ,
        !          1643: .CW sh
        !          1644: and
        !          1645: .CW if
        !          1646: statements.
        !          1647: .PP
        !          1648: The
        !          1649: .CW if
        !          1650: statement is
        !          1651: .P1
        !          1652: if \f2expression\fP then { \f2anything\fP } else { \f2anything\fP }
        !          1653: .P2
        !          1654: where the
        !          1655: .CW else
        !          1656: clause is optional.
        !          1657: The
        !          1658: .IT expression
        !          1659: may use the usual relational operators:
        !          1660: .CW == ,
        !          1661: .CW != ,
        !          1662: .CW > ,
        !          1663: .CW >= ,
        !          1664: .CW < ,
        !          1665: .CW <= ,
        !          1666: .CW && ,
        !          1667: and
        !          1668: .CW || .
        !          1669: .P1
        !          1670: pi = atan2(0,-1)
        !          1671: for i = 0 to pi by 0.1 do {
        !          1672:        if (s = sin(i)) > 0.8 then { s = 0.8 }
        !          1673:        "x" at i/2, s/2
        !          1674: }
        !          1675: .P2
        !          1676: .PS
        !          1677: .ps -2
        !          1678: pi = atan2(0,-1)
        !          1679: for i = 0 to pi by 0.1 do {
        !          1680:        if (s = sin(i)) > 0.8 then { s = 0.8 }
        !          1681:        "x" at i/2, s/2
        !          1682: }
        !          1683: .ps +2
        !          1684: .PE
        !          1685: A string comparison using
        !          1686: .CW ==
        !          1687: or
        !          1688: .CW !=
        !          1689: is also permitted, to compare quoted strings:
        !          1690: .P1
        !          1691: if "\f2string1\fP" == "\f2string2\fP" then ...
        !          1692: .P2
        !          1693: .NH
        !          1694: \fITroff\fP Interface
        !          1695: .PP
        !          1696: .IT Pic
        !          1697: is usually run as a
        !          1698: .IT troff
        !          1699: preprocessor:
        !          1700: .P1
        !          1701: pic file | troff -ms
        !          1702: .P2
        !          1703: Run it before
        !          1704: .IT eqn
        !          1705: if it is also present.
        !          1706: .PP
        !          1707: If the
        !          1708: .CW .PS
        !          1709: line looks like
        !          1710: .P1
        !          1711: \&.PS <file
        !          1712: .P2
        !          1713: then the contents of 
        !          1714: .CW file
        !          1715: are inserted in place of the
        !          1716: .CW .PS
        !          1717: line,
        !          1718: whether or not the file contains
        !          1719: .CW .PS
        !          1720: or
        !          1721: .CW .PE .
        !          1722: (This feature is deprecated in favor of the
        !          1723: .CW copy
        !          1724: statement.)
        !          1725: .PP
        !          1726: .IT Pic
        !          1727: copies the
        !          1728: .CW .PS
        !          1729: and
        !          1730: .CW .PE
        !          1731: lines from input to output intact,
        !          1732: except that it adds two things on the same line as the
        !          1733: .CW .PS :
        !          1734: .P1
        !          1735: \&.PS h w
        !          1736: .P2
        !          1737: .CW h
        !          1738: and
        !          1739: .CW w
        !          1740: are the picture height and width in units.
        !          1741: The
        !          1742: .CW -ms
        !          1743: macro package has definitions for
        !          1744: .CW .PS
        !          1745: and
        !          1746: .CW .PE
        !          1747: that cause
        !          1748: pictures to be centered and offset a bit from surrounding text.
        !          1749: (See the appendix.)
        !          1750: .PP
        !          1751: If 
        !          1752: .CW .PF '' ``
        !          1753: is used instead of
        !          1754: .CW .PE ,
        !          1755: the position after printing is restored to where
        !          1756: it was before the picture started, instead of being at the bottom.
        !          1757: .CW F '' (``
        !          1758: is for ``flyback.'')
        !          1759: .PP
        !          1760: Any input line that begins with a
        !          1761: period is assumed to be a
        !          1762: .IT troff
        !          1763: command that makes sense at that point;
        !          1764: it is copied to the output at that point in the document.
        !          1765: It is asking for trouble to add vertical space or in any way fiddle with
        !          1766: the line spacing here,
        !          1767: but point size and font changes are generally harmless:
        !          1768: .P1
        !          1769: \&.ps 24
        !          1770: circle radius .4 at 0,0
        !          1771: \&.ps 12
        !          1772: circle radius .2 at 0,0
        !          1773: \&.ps 8
        !          1774: circle radius .1 at 0,0
        !          1775: \&.ps 6
        !          1776: circle radius .05 at 0,0
        !          1777: \&.ps 10       \e" don't forget to restore size
        !          1778: .P2
        !          1779: .PS
        !          1780: .ps 24
        !          1781: circle radius .4 at 0,0
        !          1782: .ps 12
        !          1783: circle radius .2 at 0,0
        !          1784: .ps 8
        !          1785: circle radius .1 at 0,0
        !          1786: .ps 6
        !          1787: circle radius .05 at 0,0
        !          1788: .ps 10 \" don't forget to restore size
        !          1789: .PE
        !          1790: .IT Pic
        !          1791: does preserve the state of 
        !          1792: .IT troff 's
        !          1793: fill mode across pictures.
        !          1794: .PP
        !          1795: It is also safe to include sizes, fonts and local motions
        !          1796: within quoted strings
        !          1797: .CW \&"..." ) (
        !          1798: in
        !          1799: .IT pic ,
        !          1800: so long as whatever changes are made are unmade before exiting the string.
        !          1801: For example, to print text in Helvetica Bold 2 points larger:
        !          1802: .P1
        !          1803: ellipse "\es+2\ef(HBSmile!\efP\es-2"
        !          1804: .P2
        !          1805: .PS
        !          1806: ellipse "\s+2\f(HBSmile!\fP\s-2"
        !          1807: .PE
        !          1808: This is essentially the same rule as applies in
        !          1809: .IT eqn .
        !          1810: .PP
        !          1811: There is a subtle problem with complicated equations inside
        !          1812: .IT pic
        !          1813: pictures \(em they come out wrong
        !          1814: if
        !          1815: .IT eqn
        !          1816: has to leave extra vertical space for the equation.
        !          1817: If your equation involves more than subscripts and superscripts,
        !          1818: you must add to the beginning of each equation the extra information
        !          1819: .CW "space 0" :
        !          1820: .P1
        !          1821: arrow
        !          1822: box "$space 0 {H( omega )} over {1 - H( omega )}$"
        !          1823: arrow
        !          1824: .P2
        !          1825: .EQ
        !          1826: delim $$
        !          1827: .EN
        !          1828: .PS
        !          1829: arrow
        !          1830: box "$space 0 {H( omega )} over {1 - H( omega )}$"
        !          1831: arrow
        !          1832: .PE
        !          1833: .NH
        !          1834: Some Examples
        !          1835: .PP
        !          1836: Here are a handful of larger examples:
        !          1837: .KS
        !          1838: .PS
        !          1839: define ndblock X
        !          1840:        box wid boxwid/2 ht boxht/2
        !          1841:        down;  box same with .t at bottom of last box;   box same
        !          1842: X
        !          1843: .ps -2
        !          1844: .ft CW
        !          1845: boxht = .2; boxwid = .3; dx = 0.05
        !          1846: down; box; box; box; box ht 3*boxht "." "." "."
        !          1847: L: box; box; box invis wid 2*boxwid "hashtab:" with .e at 1st box .w
        !          1848: right
        !          1849: Start: box wid .5 with .sw at 1st box.ne + (.4,.2) "..."
        !          1850: N1: box wid .2 "n1";  D1: box wid .3 "d1"
        !          1851: N3: box wid .4 "n3";  D3: box wid .3 "d3"
        !          1852: box wid .4 "..."
        !          1853: N2: box wid .5 "n2";  D2: box wid .2 "d2"
        !          1854: 
        !          1855: arrow right from 2nd box 
        !          1856: ndblock
        !          1857: spline -> right .2 from 3rd last box then to N1.sw + (dx,0)
        !          1858: spline -> right .3 from 2nd last box then to D1.sw + (dx,0)
        !          1859: arrow right from last box
        !          1860: ndblock
        !          1861: spline -> right .2 from 3rd last box to N2.sw-(dx,.2) to N2.sw+(dx,0)
        !          1862: spline -> right .3 from 2nd last box to D2.sw-(dx,.2) to D2.sw+(dx,0)
        !          1863: arrow right 2*linewid from L
        !          1864: ndblock
        !          1865: spline -> right .2 from 3rd last box to N3.sw + (dx,0)
        !          1866: spline -> right .3 from 2nd last box to D3.sw + (dx,0)
        !          1867: 
        !          1868: circlerad = .3
        !          1869: circle invis "ndblock"  at last box.e + (1.2,.2)
        !          1870: arrow dashed from last circle.w to last box chop 0 chop .3
        !          1871: 
        !          1872: box invis wid 2*boxwid "ndtable:" with .e at Start.w
        !          1873: .ps
        !          1874: .ft
        !          1875: .PE
        !          1876: .KE
        !          1877: .sp
        !          1878: .P1
        !          1879: .vs -1p
        !          1880: define ndblock {
        !          1881:        box wid boxwid/2 ht boxht/2
        !          1882:        down;  box same with .t at bottom of last box;   box same
        !          1883: }
        !          1884: boxht = .2; boxwid = .3; circlerad = .3; dx = 0.05
        !          1885: down; box; box; box; box ht 3*boxht "." "." "."
        !          1886: L: box; box; box invis wid 2*boxwid "hashtab:" with .e at 1st box .w
        !          1887: right
        !          1888: Start: box wid .5 with .sw at 1st box.ne + (.4,.2) "..."
        !          1889: N1: box wid .2 "n1";  D1: box wid .3 "d1"
        !          1890: N3: box wid .4 "n3";  D3: box wid .3 "d3"
        !          1891: box wid .4 "..."
        !          1892: N2: box wid .5 "n2";  D2: box wid .2 "d2"
        !          1893: arrow right from 2nd box 
        !          1894: ndblock
        !          1895: spline -> right .2 from 3rd last box then to N1.sw + (dx,0)
        !          1896: spline -> right .3 from 2nd last box then to D1.sw + (dx,0)
        !          1897: arrow right from last box
        !          1898: ndblock
        !          1899: spline -> right .2 from 3rd last box to N2.sw-(dx,.2) to N2.sw+(dx,0)
        !          1900: spline -> right .3 from 2nd last box to D2.sw-(dx,.2) to D2.sw+(dx,0)
        !          1901: arrow right 2*linewid from L
        !          1902: ndblock
        !          1903: spline -> right .2 from 3rd last box to N3.sw + (dx,0)
        !          1904: spline -> right .3 from 2nd last box to D3.sw + (dx,0)
        !          1905: circlerad = .3
        !          1906: circle invis "ndblock"  at last box.e + (1.2,.2)
        !          1907: arrow dashed from last circle.w to last box chop 0 chop .3
        !          1908: box invis wid 2*boxwid "ndtable:" with .e at Start.w
        !          1909: .P2
        !          1910: .sp
        !          1911: .KS
        !          1912: .PS 5
        !          1913: .ps 8
        !          1914: boxht = .5; boxwid = .75
        !          1915: circlerad = .25
        !          1916:        arrow "source" "code"
        !          1917: LA:    box "lexical" "analyzer"
        !          1918:        arrow "tokens" above
        !          1919: P:     box "parser"
        !          1920:        arrow "intermediate" "code"
        !          1921: Sem:   box "semantic" "checker"
        !          1922:        arrow
        !          1923: 
        !          1924:        arrow <-> up from top of LA
        !          1925: LC:    box "lexical" "corrector"
        !          1926:        arrow <-> up from top of P
        !          1927: Syn:   box "syntactic" "corrector"
        !          1928:        arrow up
        !          1929: DMP:   box "diagnostic" "message" "printer"
        !          1930:        arrow <-> right  from right of DMP
        !          1931: ST:    box "symbol" "table"
        !          1932:        arrow from LC.ne to DMP.sw
        !          1933:        arrow from Sem.nw to DMP.se
        !          1934:        arrow <-> from Sem.top to ST.bot
        !          1935: .PE
        !          1936: .KE
        !          1937: .LP
        !          1938: .P1
        !          1939: \&.PS 5
        !          1940: \&.ps 8
        !          1941: \&     arrow "source" "code"
        !          1942: \&LA:  box "lexical" "analyzer"
        !          1943: \&     arrow "tokens" above
        !          1944: \&P:   box "parser"
        !          1945: \&     arrow "intermediate" "code"
        !          1946: \&Sem: box "semantic" "checker"
        !          1947: \&     arrow
        !          1948: \&
        !          1949: \&     arrow <-> up from top of LA
        !          1950: \&LC:  box "lexical" "corrector"
        !          1951: \&     arrow <-> up from top of P
        !          1952: \&Syn: box "syntactic" "corrector"
        !          1953: \&     arrow up
        !          1954: \&DMP: box "diagnostic" "message" "printer"
        !          1955: \&     arrow <-> right  from right of DMP
        !          1956: \&ST:  box "symbol" "table"
        !          1957: \&     arrow from LC.ne to DMP.sw
        !          1958: \&     arrow from Sem.nw to DMP.se
        !          1959: \&     arrow <-> from Sem.top to ST.bot
        !          1960: \&.PE
        !          1961: .P2
        !          1962: .PP
        !          1963: There are eighteen objects (boxes and arrows) in the picture,
        !          1964: and one line of
        !          1965: .IT pic
        !          1966: input for each;
        !          1967: this seems like an acceptable level of verbosity.
        !          1968: .sp
        !          1969: .KS
        !          1970: .PS
        !          1971: .ps -2
        !          1972:        circle "DISK"
        !          1973:        arrow "character" "defns"
        !          1974: CPU:   box "CPU" "(16-bit mini)"
        !          1975:        { arrow <- from top of CPU up "input " rjust }
        !          1976:        arrow
        !          1977: CRT:   "   CRT" ljust
        !          1978:        line from CRT - 0,0.075 up 0.15 \
        !          1979:                then right 0.5 \
        !          1980:                then right 0.5 up 0.25 \
        !          1981:                then down 0.5+0.15 \
        !          1982:                then left 0.5 up 0.25 \
        !          1983:                then left 0.5
        !          1984: Paper: CRT + 1.05,0.75
        !          1985:        arrow <- from Paper down 1.5
        !          1986:        " ...  paper" ljust at end of last arrow + 0, 0.25
        !          1987:        circle rad 0.05 at Paper + (-0.055, -0.25)
        !          1988:        circle rad 0.05 at Paper + (0.055, -0.25)
        !          1989:        "   rollers" ljust at Paper + (0.1, -0.25)
        !          1990: .ps +2
        !          1991: .PE
        !          1992: .ce
        !          1993: Basic Digital Typesetter
        !          1994: .sp
        !          1995: .KE
        !          1996: .LP
        !          1997: .P1
        !          1998: .vs -1
        !          1999: \&.PS
        !          2000: \&.ps -2
        !          2001:        circle "DISK"
        !          2002:        arrow "character" "defns"
        !          2003: CPU:   box "CPU" "(16-bit mini)"
        !          2004:        { arrow <- from top of CPU up "input " rjust }
        !          2005:        arrow
        !          2006: CRT:   "   CRT" ljust
        !          2007:        line from CRT - 0,0.075 up 0.15 \e
        !          2008:                then right 0.5 \e
        !          2009:                then right 0.5 up 0.25 \e
        !          2010:                then down 0.5+0.15 \e
        !          2011:                then left 0.5 up 0.25 \e
        !          2012:                then left 0.5
        !          2013: Paper: CRT + 1.05,0.75
        !          2014:        arrow <- from Paper down 1.5
        !          2015:        " ...  paper" ljust at end of last arrow + 0, 0.25
        !          2016:        circle rad 0.05 at Paper + (-0.055, -0.25)
        !          2017:        circle rad 0.05 at Paper + (0.055, -0.25)
        !          2018:        "   rollers" ljust at Paper + (0.1, -0.25)
        !          2019: \&.ps +2
        !          2020: \&.PE
        !          2021: \&.ce
        !          2022: \&Basic Digital Typesetter
        !          2023: .P2
        !          2024: .SH
        !          2025: Acknowledgements
        !          2026: .PP
        !          2027: I am indebted to Chris Van Wyk for ideas from several versions of
        !          2028: .IT ideal .
        !          2029: He and Doug McIlroy have also contributed algorithms
        !          2030: for line and circle drawing,
        !          2031: and made useful suggestions on the design of
        !          2032: .IT pic .
        !          2033: Theo Pavlidis contributed the basic spline algorithm;
        !          2034: Eric Grosse provided code to compute the bounding box of an arc.
        !          2035: Charles Wetherell pointed out reference
        !          2036: [2]
        !          2037: to me, and made several valuable criticisms on an early
        !          2038: draft of the language and manual.
        !          2039: The exposition in this manual has been greatly improved
        !          2040: by suggestions from Jim Blinn and Mark Miller.
        !          2041: I am grateful to
        !          2042: my early users \(em
        !          2043: Brenda Baker,
        !          2044: Dottie Luciani,
        !          2045: and Paul Tukey
        !          2046: \(em
        !          2047: for their suggestions and cheerful use of
        !          2048: an often shaky and clumsy system.
        !          2049: .PP
        !          2050: More recent versions of
        !          2051: .IT pic
        !          2052: have benefited greatly from
        !          2053: adventurous use by
        !          2054: Jon Bentley and Ravi Sethi;
        !          2055: their comments on the manual are also much appreciated.
        !          2056: .SH
        !          2057: References
        !          2058: .LP
        !          2059: |reference_placement
        !          2060: .BP
        !          2061: ........
        !          2062: .SH
        !          2063: Appendix A:  \fIPic\fP Reference Manual
        !          2064: .SH
        !          2065: Pictures
        !          2066: .PP
        !          2067: The top-level object in
        !          2068: .IT pic
        !          2069: is the ``picture'':
        !          2070: .P1
        !          2071: \f2picture\fP:
        !          2072:        .PS \f2optional-width\fP \f2optional-height\fP
        !          2073:        \f2element-list\fP
        !          2074:        .PE
        !          2075: .P2
        !          2076: If
        !          2077: .IT optional-width
        !          2078: is present, the picture is made that many inches wide,
        !          2079: regardless of any dimensions used internally.
        !          2080: The height is scaled in the same proportion unless
        !          2081: .IT optional-height
        !          2082: is present.
        !          2083: If instead the line is
        !          2084: .P1
        !          2085: \&.PS <f
        !          2086: .P2
        !          2087: the file
        !          2088: .CW f
        !          2089: is inserted in place of the
        !          2090: .CW .PS
        !          2091: line.
        !          2092: If
        !          2093: .CW .PF
        !          2094: is used instead of
        !          2095: .CW .PE ,
        !          2096: the position after printing is restored to what it was
        !          2097: upon entry.
        !          2098: .PP
        !          2099: In no case will the picture be larger than
        !          2100: .CW maxpsht
        !          2101: \(mu
        !          2102: .CW maxpswid .
        !          2103: .SH
        !          2104: Elements
        !          2105: .PP
        !          2106: An
        !          2107: .IT element-list
        !          2108: is a list of elements (what else?);
        !          2109: the elements are
        !          2110: .P1
        !          2111: \f2element\fP:
        !          2112:        \f2primitive  attribute-list\fP
        !          2113:        \f2placename\fP : \f2element\fP
        !          2114:        \f2placename\fP : \f2position\fP
        !          2115:        \f2var\fP = \f2expr\fP
        !          2116:        \f2direction\fP
        !          2117:        { \f2element-list\fP }
        !          2118:        [ \f2element-list\fP ]
        !          2119:        for \f2var\fP = \f2expr\fP to \f2expr\fP by \f2expr\fP do { \f2anything\fP }
        !          2120:        if \f2expr\fP then { \f2anything\fP } else { \f2anything\fP }
        !          2121:        copy \f2file\fP
        !          2122:        copy thru \f2macro\fP
        !          2123:        copy \f2file\fP thru \fPmacro\fP
        !          2124:        sh { \f2commandline\fP }
        !          2125:        print \f2expr\fP
        !          2126:        reset \f2optional var-list\fP
        !          2127:        \f2troff-command\fP
        !          2128: .P2
        !          2129: .PP
        !          2130: Elements are separated by newlines or semicolons;
        !          2131: a long element may be continued by ending the line with a backslash.
        !          2132: Comments are introduced by a
        !          2133: .CW #
        !          2134: and terminated by a newline.
        !          2135: .PP
        !          2136: Variable names begin with a lower case letter;
        !          2137: place names begin with upper case.
        !          2138: Place and variable names retain their values
        !          2139: from one picture to the next.
        !          2140: .PP
        !          2141: The current position and direction of motion are saved upon entry
        !          2142: to a
        !          2143: .CW {...}
        !          2144: block and restored upon exit.
        !          2145: .PP
        !          2146: Elements within a block enclosed in
        !          2147: .CW [...]
        !          2148: are treated as a unit;
        !          2149: the dimensions are determined by the extreme points
        !          2150: of the contained objects.
        !          2151: Names, variables, and direction of motion within a block are local to that block.
        !          2152: .PP
        !          2153: .IT troff-command
        !          2154: is any line that begins with a period.
        !          2155: Such a line is assumed to make sense in the context where it appears;
        !          2156: accordingly,
        !          2157: if it doesn't work, don't call.
        !          2158: .SH
        !          2159: Primitives
        !          2160: .PP
        !          2161: The primitive objects are
        !          2162: .P1
        !          2163: \f2primitive\fP:
        !          2164:        box
        !          2165:        circle
        !          2166:        ellipse
        !          2167:        arc
        !          2168:        line
        !          2169:        arrow
        !          2170:        spline
        !          2171:        move
        !          2172:        \f2text-list\fP
        !          2173: .P2
        !          2174: .CW arrow
        !          2175: is a synonym for
        !          2176: .CW line
        !          2177: .CW -> .
        !          2178: .SH
        !          2179: Attributes
        !          2180: .PP
        !          2181: An
        !          2182: .IT attribute-list
        !          2183: is a sequence of zero or more attributes;
        !          2184: each attribute consists of a keyword, perhaps followed by a value.
        !          2185: .P1
        !          2186: .ta .5i 2.5i
        !          2187: \f2attribute\fP:
        !          2188:        h(eigh)t \f2expr\fP     wid(th) \f2expr\fP
        !          2189:        rad(ius) \f2expr\fP     diam(eter) \f2expr\fP
        !          2190:        up \f2opt-expr\fP       down \f2opt-expr\fP
        !          2191:        right \f2opt-expr\fP    left \f2opt-expr\fP
        !          2192:        from \f2position\fP     to \f2position\fP
        !          2193:        at \f2position\fP       with \f2corner\fP
        !          2194:        by \f2expr, expr\fP     then
        !          2195:        dotted \f2opt-expr\fP   dashed \f2opt-expr\fP
        !          2196:        chop \f2opt-expr\fP     ->  <-  <->
        !          2197:        invis   solid
        !          2198:        fill \f2opt-expr\fP     same
        !          2199:        \f2text-list\fP \f2expr\fP
        !          2200: .P2
        !          2201: Missing attributes and values are filled in from defaults.
        !          2202: Not all attributes make sense for all primitives;
        !          2203: irrelevant ones are silently ignored.
        !          2204: The attribute
        !          2205: .CW at
        !          2206: causes the geometrical center to be put at the specified place;
        !          2207: .CW with
        !          2208: causes the position on the object to be put at the specified place.
        !          2209: For lines, splines and arcs,
        !          2210: .CW height
        !          2211: and
        !          2212: .CW width
        !          2213: refer to arrowhead size.
        !          2214: A bare
        !          2215: .IT expr
        !          2216: implies motion in the current direction.
        !          2217: .SH
        !          2218: Text
        !          2219: .PP
        !          2220: Text is normally an attribute of some primitive;
        !          2221: by default it is placed at the geometrical center of the object.
        !          2222: Stand-alone text is also permitted.
        !          2223: A
        !          2224: .IT text-list
        !          2225: is a list of text items; a text item is
        !          2226: a quoted string optionally followed by positioning requests:
        !          2227: .P1
        !          2228: \f2text-item\fP:
        !          2229:        "..." \f2positioning ...\fP
        !          2230:        sprintf("\f2format\fP", \f2expr\fP, \f2...\fP) \f2positioning ...\fP
        !          2231: \f2positioning\fP:
        !          2232:        center  ljust  rjust  above  below
        !          2233: .P2
        !          2234: If there are multiple text items for some primitive,
        !          2235: they are centered vertically except as qualified.
        !          2236: Positioning requests apply to each item independently.
        !          2237: .PP
        !          2238: Text items can contain
        !          2239: .IT troff
        !          2240: commands for size and font changes, local motions, etc.,
        !          2241: but make sure that these are balanced
        !          2242: so that the entering state is restored before exiting.
        !          2243: .SH
        !          2244: Positions and places
        !          2245: .PP
        !          2246: A position is ultimately an
        !          2247: .IT x,y
        !          2248: coordinate pair, but it may be specified in other ways.
        !          2249: .P1
        !          2250: \f2position\fP:
        !          2251:        \f2expr, expr\fP
        !          2252:        \f2place\fP \(+- \f2expr, expr\fP
        !          2253:        \f2place\fP \(+- ( \f2expr, expr\fP )
        !          2254:        ( \f2position\fP,\f2 position\fP )
        !          2255:        \f2expr\fP \f2[\fPof the way\f2]\fP between \f2position\fP and \f2position\fP
        !          2256:        \f2expr\fP < \f2position\fP , \f2position\fP >
        !          2257:        ( \f2position\fP )
        !          2258: .sp .5
        !          2259: \f2place\fP:
        !          2260:        \f2placename\fP \f2optional-corner\fP
        !          2261:        \f2corner\fP of \f2placename\fP
        !          2262:        \f2nth\fP \f2primitive\fP \f2optional-corner\fP
        !          2263:        \f2corner\fP of \f2nth\fP \f2primitive\fP
        !          2264:        Here
        !          2265: .P2
        !          2266: An
        !          2267: .IT optional-corner
        !          2268: is one of the eight compass points
        !          2269: or the center or the start or end of a primitive.
        !          2270: .P1
        !          2271: \f2optional-corner\fP:
        !          2272:        .n  .e  .w  .s  .ne  .se  .nw  .sw  .c  .start  .end
        !          2273: \f2corner\fP:
        !          2274:        top  bot  left  right  start  end
        !          2275: .P2
        !          2276: Each object in a picture has an ordinal number;
        !          2277: .IT nth
        !          2278: refers to this.
        !          2279: .P1
        !          2280: \f2nth\fP:
        !          2281:        \f2n\fPth
        !          2282:        \f2n\fPth last
        !          2283: .P2
        !          2284: Since barbarisms like
        !          2285: .CW 1th
        !          2286: and
        !          2287: .CW 3th
        !          2288: are barbaric,
        !          2289: synonyms like
        !          2290: .CW 1st
        !          2291: and
        !          2292: .CW 3rd
        !          2293: are accepted as well.
        !          2294: .SH
        !          2295: Variables
        !          2296: .PP
        !          2297: The built-in variables and their default values are:
        !          2298: .P1
        !          2299: .ta .5i 2.5i
        !          2300:        boxwid 0.75     boxht 0.5
        !          2301:        circlerad 0.25  arcrad 0.25
        !          2302:        ellipsewid 0.75 ellipseht 0.5
        !          2303:        linewid 0.5     lineht 0.5
        !          2304:        movewid 0.5     moveht 0.5
        !          2305:        textwid 0       textht 0
        !          2306:        arrowwid 0.05   arrowht 0.1
        !          2307:        dashwid 0.1     arrowhead 2
        !          2308:        maxpsht 8.5     maxpswid 11
        !          2309:        scale 1 fillval .3
        !          2310: .P2
        !          2311: These may be changed at any time,
        !          2312: and the new values remain in force from picture to picture until changed again
        !          2313: or reset by a
        !          2314: .CW reset
        !          2315: statement.
        !          2316: Variables changed within
        !          2317: .CW [
        !          2318: and
        !          2319: .CW ]
        !          2320: revert to their previous value upon exit from the block.
        !          2321: Dimensions are divided by
        !          2322: .CW scale
        !          2323: during output.
        !          2324: .SH
        !          2325: Expressions
        !          2326: .PP
        !          2327: Expressions in
        !          2328: .IT pic
        !          2329: are evaluated in floating point.
        !          2330: All numbers representing dimensions are taken to be in inches.
        !          2331: .EQ
        !          2332: delim $$
        !          2333: .EN
        !          2334: .P1
        !          2335: \f2expr\fP:
        !          2336:        \f2expr\fP \f2op\fP \f2expr\fP
        !          2337:        - \f2expr\fP
        !          2338:        ! \f2expr\fP
        !          2339:        ( \f2expr\fP )
        !          2340:        variable
        !          2341:        number
        !          2342:        \f2place\fP .x
        !          2343:        \f2place\fP .y
        !          2344:        \f2place\fP .ht
        !          2345:        \f2place\fP .wid
        !          2346:        \f2place\fP .rad
        !          2347:        sin($expr$)  cos($expr$)  atan2($expr,expr$)  log($expr$)  exp($expr$)
        !          2348:        sqrt($expr$)  max($expr,expr$)  min($expr,expr$)  int($expr$)  rand()
        !          2349: \f2op\fP:
        !          2350:        +  -   *  /   %   ^
        !          2351:        <  <=  >  >=  ==  !=  &&  ||
        !          2352: .P2
        !          2353: .SH
        !          2354: Definitions
        !          2355: .PP
        !          2356: The
        !          2357: .CW define
        !          2358: and
        !          2359: .CW undef
        !          2360: statements are not part of the grammar.
        !          2361: .P1
        !          2362: \f2define\fP:
        !          2363:        define \f2name\fP { \f2replacement text\fP }
        !          2364: \f2undef\fP:
        !          2365:        undef \f2name\fP
        !          2366: .P2
        !          2367: .EQ
        !          2368: delim off
        !          2369: .EN
        !          2370: Occurrences of
        !          2371: .CW $1 ,
        !          2372: .CW $2 ,
        !          2373: etc.,
        !          2374: in the replacement text
        !          2375: will be replaced by the corresponding arguments if
        !          2376: .IT name
        !          2377: is invoked as
        !          2378: .P1
        !          2379: \f2name\fP(\f2arg1\fP, \f2arg2\fP, ...)
        !          2380: .P2
        !          2381: Non-existent arguments are replaced by null strings.
        !          2382: .IT Replacement
        !          2383: .IT text
        !          2384: may contain newlines.
        !          2385: The
        !          2386: .CW undef
        !          2387: statement removes the definition of a macro.
        !          2388: .SH
        !          2389: The .PS and .PE Macros
        !          2390: .PP
        !          2391: This is the default definition of the
        !          2392: .CW .PS
        !          2393: and
        !          2394: .CW .PE
        !          2395: macros:
        !          2396: .P1
        !          2397:  .de PS        \e" start picture; $1 is height, $2 is width, in inches
        !          2398:  .sp .3
        !          2399:  .in (\e\en(.lu-\e\e$2)/2u
        !          2400:  .ne \e\e$1
        !          2401:  ..
        !          2402:  .de PE        \e" end of picture
        !          2403:  .in
        !          2404:  .sp .6
        !          2405:  ..
        !          2406: .P2
        !          2407: .SH
        !          2408: Summary of Features Added Since Original Version
        !          2409: .PP
        !          2410: The built-in functions
        !          2411: .CW sin ,
        !          2412: .CW cos ,
        !          2413: .CW atan2 ,
        !          2414: .CW log ,
        !          2415: .CW exp ,
        !          2416: .CW sqrt ,
        !          2417: .CW max ,
        !          2418: .CW min ,
        !          2419: .CW int ,
        !          2420: and
        !          2421: .CW rand
        !          2422: are available.
        !          2423: .PP
        !          2424: The
        !          2425: .CW copy
        !          2426: statement includes data from a file or that follows immediately:
        !          2427: .P1
        !          2428: copy "\f2filename\fP"
        !          2429: copy thru \f2macro\fP
        !          2430: copy "\f2filename\fP" thru \f2macro\fP
        !          2431: .P2
        !          2432: The
        !          2433: .IT macro
        !          2434: may be either the name of a defined macro, or the body of a macro
        !          2435: enclosed in braces.
        !          2436: If no filename is given,
        !          2437: .CW copy
        !          2438: copies the input until the next
        !          2439: .CW .PE .
        !          2440: .PP
        !          2441: The
        !          2442: .CW for
        !          2443: and
        !          2444: .CW if
        !          2445: statements provide loops and decision-making:
        !          2446: .P1
        !          2447: for \f2var\fP=\f2expr\fP to \f2expr\fP by \f2expr\fP do { \f2anything\fP }
        !          2448: if \f2expr\fP then { \f2anything\fP } else { \f2anything\fP }
        !          2449: .P2
        !          2450: The
        !          2451: .CW by
        !          2452: and
        !          2453: .CW else
        !          2454: clauses are optional.
        !          2455: The
        !          2456: .IT expr
        !          2457: in an
        !          2458: .CW if
        !          2459: may use the usual relational operators
        !          2460: or the tests
        !          2461: .IT str1
        !          2462: .CW ==
        !          2463: (or
        !          2464: .CW != )
        !          2465: .IT str2
        !          2466: for two quoted strings.
        !          2467: .PP
        !          2468: The
        !          2469: .CW sh
        !          2470: command executes any sequence of commands, after expanding any defined names:
        !          2471: .P1
        !          2472: sh { \f2anything\fP }
        !          2473: .P2
        !          2474: .PP
        !          2475: In all of the above,
        !          2476: any single character that does not occur within the body
        !          2477: may be used to enclose a body,
        !          2478: instead of
        !          2479: braces, as in
        !          2480: .P1
        !          2481: define name X replacement text X
        !          2482: .P2
        !          2483: .PP
        !          2484: Text strings are first-class citizens:
        !          2485: a statement beginning with a sequence of text strings is treated
        !          2486: as an invisible box with the strings positioned at its center.
        !          2487: The variable
        !          2488: .CW textht
        !          2489: and
        !          2490: .CW textwid
        !          2491: may be set to any values to control positioning.
        !          2492: The height of \f2n\fP such strings is \f2n\fP \(mu
        !          2493: .CW textht .
        !          2494: .PP
        !          2495: It is possible to convert expressions to formatted strings:
        !          2496: .P1
        !          2497: sprintf("\f2format\fP", \f2expr\fP, \f2expr\fP, ...)
        !          2498: .P2
        !          2499: is equivalent to a quoted string in any context.
        !          2500: Variants of
        !          2501: .CW %f
        !          2502: and
        !          2503: .CW %g
        !          2504: are the only sensible format conversions.
        !          2505: .PP
        !          2506: Built-in variables may be reset to default values with
        !          2507: .CW reset .
        !          2508: .PP
        !          2509: The
        !          2510: .CW undef
        !          2511: statement removes a macro definition.
        !          2512: .PP
        !          2513: Arrowheads may be filled with the 
        !          2514: .CW arrowhead
        !          2515: variable;
        !          2516: their positioning is improved on arcs.
        !          2517: .PP
        !          2518: The width and height of the generated picture
        !          2519: may be set independently from the
        !          2520: .CW .PS
        !          2521: line;
        !          2522: the maximum height and width are set from
        !          2523: .CW maxpsht 
        !          2524: and
        !          2525: .CW maxpswid .
        !          2526: .PP
        !          2527: The state of
        !          2528: .IT troff 's
        !          2529: fill or no-fill mode is preserved around a picture.
        !          2530: .PP
        !          2531: Input numbers may be expressed in
        !          2532: .CW E
        !          2533: notation.
        !          2534: .PP
        !          2535: Numerous internal changes have been made as well.
        !          2536: Any number of objects, text strings, etc., may be used;
        !          2537: the only limit is total available memory.
        !          2538: Output is now produced in inches instead of units
        !          2539: for a particular typesetter,
        !          2540: so the 
        !          2541: .CW -T
        !          2542: option has gone away.

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