OpenBSD-4.6/usr.bin/learn/lib/eqn/L5.1a

#once #create message
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delim $$
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.LP
So far we have carefully skirted around a potential
problem; maybe you've wondered about it.
Suppose we want to produce an equation that looks
like this:
.EQ
x sup { pi + 1 }
.EN
The superscript is complicated, in that it contains
both a $pi$ and a +1, which has to be separated
from the $pi$ by a blank.
But I already told you that a blank terminates
the superscript.  What's going on?

As the first step to finding out, will the input
equation

  x sup pi + 1

produce the output

  $x sup {pi + 1}$ ?
Answer yes or no.
(You can play with the file "Example" if you like.)
.pl 1
#once #create Example
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replace me
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.pl 1
#
#once neqn message | nroff -T$term %s/tinyms -
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5.1b