# [tex-k] inaccuracy on page 215 of The TeXbook

Tue Oct 13 12:41:54 CEST 2020

Page A215, line 26 says that expansion is suppressed
Just after a $_3 token that begins math mode, to see if another$_3 follows.
However, any character whose category code is 3 would do, not
just $_3. For example, the following program \catcode\!=3 \catcode\?=13 \def?{!} !?math!? \bye typesets the equivalent of$ $math$ \$ instead of $$math$$.

----

Previous reports:
https://github.com/dine2014/texbook-mfbook-bugs/blob/master/bugs.md

(I don't know if I can go through every page before Nov 1...)