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How do I put the "$_" string in a \section?

When I try \section{$\_} it gives me Missing $ inserted error.

When I try \section{\$\_} it gives me Extra }, or forgotten $. error.

When I try \section{\verb|$_|} it gives me Argument of \@xtrplargoom has an extra } error.

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do you mean a real dollar sign, or the section sign? – barbara beeton Jan 13 '12 at 20:24
I mean the real dollar sign followed by an underscore. (Perl's $_ variable.) – Peteris Krumins Jan 13 '12 at 20:24
@ChristianLindig see my 3rd "when" case. """ When I try \section{\verb|$_|} it gives me Argument of \@xtrplargoom has an extra } error. """ (I'm using memoir document class.) – Peteris Krumins Jan 13 '12 at 20:25
The second is correct and doesn't give errors. You may want to say \texttt{\$\_}, but it's not relevant. – egreg Jan 13 '12 at 20:26
I can't explain it guys, but it started working by itself. Sorry about trouble! – Peteris Krumins Jan 13 '12 at 20:39

2 Answers 2

Not an answer, but an explanation:

  • "When I try \section{$\_} it gives me Missing $ inserted error."

    You are allowed math in \section, so \section{This is $x$} is no problem. In your case however, you don't have a closing $. Sure, you may not want it, but that's what TeX sees and therefore expects.

  • "When I try \section{\$\_} it gives me Extra }, or forgotten $ error."

    This works because escaping $ and _ removes their math-context.

  • "When I try \section{\verb|$_|} it gives me Argument of \@xtrplargoom has an extra } error."

    You cannot pass verbatim content as an argument to a macro. See Why doesn’t verbatim work within ...? The link includes ways of using verbatim content as arguments in a number of ways, if that's what you're really after.

When working with hyperref, you may also be interested in using \texorpdfstring{<TeX string>}{<PDF string>}. This is helpful if you have bookmarks (also associated with \section commands) that consist of a string containing ASCII characters.

And another question:

  • Why is it that sometimes it could not work and then suddenly work?

    Well, when you use \section{<stuff>}, LaTeX actually does \section[<stuff>]{<stuff>} (since the complete syntax of the optional argument is used, even though you don't specify it). Therefore, <stuff> makes its way into your .aux file, used for processing labels, references and other ToC-related things. If "bad things" go in there, it could be that it takes a "correct" compile to clear it (even though there will still be errors from reading the "bad" .aux), followed by another "correct" compile to be error-free. When in doubt, you could start fresh by deleting the .aux file before compiling.

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+1 for the explanation about the aux file. I think that this is what happened to Peteris. – Bruno Le Floch Jan 14 '12 at 0:40

Okay, the \section{\$\_} works this fine. I closed and opened the tex file and it started working by itself.

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