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When using the \pmod command as a subscript to a sum, I often encounter some extra unwanted space. For example, writing

\[ \sum_{n \equiv 1 \pmod{k}} ... \]

produces the following image:

enter image description here

Does anyone have any ideas to delete the extra white space between the 1 and the open parenthesis?

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up vote 14 down vote accepted

I'd define a variant of \pmod:

\def\@pmods#1{\mkern4mu({\operator@font mod}\mkern 6mu#1)}

You can use \pmod as before in all other situations and write

\[ \sum_{n \equiv 1 \pmod*{k}} ... \]

when you need it as a subscript to a sum.

enter image description here

Another way might be to load amsmath and redefine \pod (\pmod is defined in terms of it):

  {\if@display \mkern 18mu\else \mkern 8mu\fi (#1)}
  {\if@display \mkern 18mu\else \mkern 8mu\fi (#1)}

This will avoid having to say \pmod* and the result will be the same as shown.

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This works great. Thanks for your help! – JavaMan Dec 24 '11 at 3:10
egreg, shouldn't the \allowbreak go before the \mathchoice? I was just looking at your comment on Andrew Swann's answer here: tex.stackexchange.com/questions/255584/… – justin Aug 3 '15 at 20:23
@justin You're perfectly right! – egreg Aug 3 '15 at 20:28

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