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This question already has an answer here:

I want to let the command \old| refer to the command \| (which produces the output ||.) So I do:

\let\old|\|

LaTeX complains "Missing $ inserted." How can I fix it?

marked as duplicate by yo', Marco Daniel, Mensch, Stefan Kottwitz Mar 2 '13 at 22:05

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  • Use \def\old#1{\|} and than you can work with \old| – Marco Daniel Mar 2 '13 at 20:01
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    A command name is (in default setting) either \<one-char> or \<arbitrary-number-of-letters>. The character | is not a letter. I suggest using \let\oldvert\| . – yo' Mar 2 '13 at 20:04

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