Norm symbol in subscripts of index

Question

I found this related topic but it didn't seem to fix my problem: How to fix symbol index entry?

I was using good old \|\cdot\| for norms but my index wasn't liking it. So then I did the new command \norm to be \|. This works great except in subscripts. To be specific I have something like this:

{\index[symbols]{$B_{\norm\cdot\norm}(x,r)$}}

And it appears in the index as $B_{weird stuff}(x,r)$ . More specifically, going into the index file I see it's recorded as this:

$B_{\delimiter 026B30D \cdot \delimiter 026B30D }(x,r)$

Any ideas?

Welcome to TeX.sx! A tip: If you indent lines by 4 spaces or [enclose words in backticks ```](http://meta.tex.stackexchange.com/q/863), they'll be marked as code, as can be seen in my edit. You can also highlight the code and click the "code" button (with "{}" on it). — Guido, Feb 25 '13 at 13:31
What happens with \DeclareRobustCommand*{\norm}{\|}? (to be used in math mode) — , Feb 25 '13 at 13:51
@danzibr: I will make it into an answer so that you can accept it and help me get all the reputation I deserve ;-) — , Feb 25 '13 at 16:11

score 3 · Answer 1 · answered Feb 25 '13 at 16:16

The phenomenon is an instance of TeX "expanding" things. Sometimes you do not want this to happen: this is discussed in LaTeX: a document preparation system under the name of fragile and robust commands. One way to make things "robust" is to use \DeclareRobustCommand: so here

\DeclareRobustCommand*{\norm}{\|}

can be used to solve your problem.

Norm symbol in subscripts of index

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