import BTL learn(1) lessons/eqn

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+#once #create message
+.ND
+.PP
+Now that we have some of the preliminaries out of the way,
+we can get on to doing real mathematics.
+I have been slipping small things into the example files
+as we go along so that you will at least have seen
+some common neqn constructions.
+
+One of the most frequent is the word "sub", which
+indicates a subscript, like this:
+
+   .EQ
+   x sub i + y sub j
+   .EN
+
+which produces
+.EQ
+x sub i + y sub j
+.EN
+The main thing to notice is that the blanks are delimiters -
+the subscript of "x" is "i"; the blank after the "i" marks
+the end of the subscript.
+
+Modify the file "Example" so the equation in it looks like
+this:
+.EQ
+x sub alpha ~=~ y sub pi ~+~ z sub pi
+.EN
+Then type "ready".
+.pl 1
+#once #create Ref
+.LP
+.EQ
+x sub alpha ~=~ y sub pi ~+~ z sub pi
+.EN
+.pl 1
+#once #create Example
+.LP
+.EQ
+xxx
+.EN
+.pl 1
+#
+#once neqn Ref | nroff >X1 &
+#once neqn message | nroff -T$term %s/tinyms -
+#user
+neqn Example | nroff >X2
+#cmp X1 X2
+#log
+#next
+3.1b 10
+3.2a 5