4.3BSD-Tahoe/usr/lib/learn/eqn/L7.2c

#once #create message
.ND
.tr %$
.EQ
delim $$
.EN
.LP
Modify file "Example" so it looks like this,
then type "ready".
.pl 1
#once #create Ref
.LP
.EQ
sum to N+n-m x sub mn > 0
.EN
.pl 1
#once #create Example
.LP
.EQ
xxx
.EN
.pl 1
#once neqn Ref | nroff >X1 &
#once neqn message Ref | nroff -T$term %s/tinyms -
#user
neqn Example | nroff >X2
#cmp X1 X2
#log
#next
7.1d 10