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Annotation of 43BSDTahoe/usr.lib/learn/eqn/L10.1a, revision 1.1.1.1

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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