#once #create message
.ND
.tr %$
.EQ
delim $$
.EN
.LP
So far every equation you have typed in
has been "displayed" - neatly centered or indented, and
offset from the surrounding text.
But not all equations are like that.
Very often they appear right in the middle of
running text as subscripts like $x sub i$ or special characters
like $pi$ or $partial$.  How are these done?

The idea is this.  Two characters (which may be identical)
are set aside as "delimiters".  When the
left delimiter is seen anywhere in ___any line,
it marks the beginning of an in-line equation.
The end is marked by the right delimiter.  Between the
delimiters, all the normal rules of neqn apply.

Suppose we say the delimiters are % signs.
Then to get $pi$, you have to type %pi%. 

To make sure that you can do this much, find the
$pi$, $alpha$ and $sum$ characters in "Example"
and make them into in-line equations.
Use % and % as the delimiter characters.
(This is the most frequent choice, by the way.)
Type "ready" when you're done.
.pl 1
#once #create Ref
.EQ
delim $$
.EN
.LP
This line contains some $pi$ and $alpha$ Greek
and $sum$ as well.  Don't forget that spaces
inside dollar signs are ignored, while spaces
outside them are significant.
.pl 1
#once #create Example
.EQ
delim $$
.EN
.LP
This line contains some pi and alpha Greek
and sum as well.  Don't forget that spaces
inside dollar signs are ignored, while spaces
outside them are significant.
.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
6.1b