Interdata_v6/usr/source/troff/neqn/read_me

Find at most related files.
including files from this version of Unix. 
The grammar for neqn is in ne.g; don't change it
until you're reasonably cocky.
The grammars for eqn and neqn are designed to accept
exactly the same language, and it is strongly
recommended that you keep to this principle.

Semantic actions for most kinds of things are in ne[1256].c;
input processing is in ne3.c, general control in ne4.c
(including the main routine), and
lexical stuff in nelex.c. nelex.c includes y.tab.c (from yaccing
ne.g), so if you change the grammar you have to recompile
nelex.c.

Make a new neqn with
	yacc ne.g
	cc ne*.c -ly -lp

Notice that this uses -lp, not -lS.

The file test1 is a miniature test, small enough that
you can understand what it does by eyeballing the output.
When that works, use the file aip/browman for
bigger and more serious testing.
Both eqn and neqn have an undocumented option "-" which
turns on a fair amount of debugging information related
mainly to the heights of various objects.

Regrettably, neqn is somewhat different from eqn
internally, because it has not yet been converted
to use the new standard io.