Annotation of 43BSD/usr.lib/learn/eqn/L10.1a, revision 1.1

1.1     ! root        1: #once #create message
        !             2: .ND
        !             3: .tr %$
        !             4: .EQ
        !             5: delim $$
        !             6: .EN
        !             7: .LP
        !             8: The next topic goes back to the problem of formatting
        !             9: equations on the page.  Sometimes it is desirable to
        !            10: line up one part of an equation with some part
        !            11: of a previous equation - for example, equals signs
        !            12: are often lined up like this:
        !            13: .EQ I
        !            14: x mark = y sub i
        !            15: .EN
        !            16: .EQ I
        !            17: lineup = z sub i
        !            18: .EN
        !            19: .EQ I
        !            20: x sub i + y sub i lineup = z sub i
        !            21: .EN
        !            22: 
        !            23: To achieve this, you have to do several things.
        !            24: (1) tell neqn to remember the place where things are
        !            25: to be lined up, which is done by saying
        !            26: "mark" just before the thing you want remembered:
        !            27:   .EQ I
        !            28:   x mark = y sub i
        !            29:   .EN
        !            30: .br
        !            31: (2) Then, in successive equations, telling neqn
        !            32: to line up something on the previous mark, with
        !            33: "lineup":
        !            34:    .EQ I
        !            35:    lineup = z sub i
        !            36:    .EN
        !            37: .br
        !            38: (3) You ____have __to use either ".EQ I" or ".EQ L";
        !            39: you can't line things up in a centered equation.
        !            40: 
        !            41: For practice, modify "Example" so the
        !            42: equations are lined up on the equals signs, then
        !            43: type "ready".
        !            44: .pl 1
        !            45: #once #create Ref
        !            46: .LP
        !            47: A test of mark and lineup:
        !            48: .EQ I
        !            49: x sub i ~ mark =~ 1
        !            50: .EN
        !            51: .EQ I
        !            52: x sub i + y sub i ~ lineup = ~2
        !            53: .EN
        !            54: .pl 1
        !            55: #once #create Example
        !            56: .LP
        !            57: A test of mark and lineup:
        !            58: .EQ I
        !            59: x sub i ~ =~ 1
        !            60: .EN
        !            61: .EQ I
        !            62: x sub i + y sub i ~ =~ 2
        !            63: .EN
        !            64: .pl 1
        !            65: #
        !            66: #once neqn Ref | nroff >X1 &
        !            67: #once neqn message Ref | nroff -T$term %s/tinyms -
        !            68: #user
        !            69: neqn Example | nroff >X2
        !            70: #cmp X1 X2
        !            71: #fail
        !            72: Don't forget that tilde is a real character;
        !            73: put the mark and lineup after it.
        !            74: Remember .EQ I.
        !            75: #log
        !            76: #next
        !            77: 10.1b 10

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