I want to use \middle| inside of brackets like this.


  \left\{\frac{1}{n} \middle| n>0\right\}



But this examples lacks space before and after the mid |. I don't want to write every time:

left\{\frac{1}{n} \;\middle|\; n>0\right\}

How can I redefine the \middle| command to mean \;\middle|\;? I tried




but neither works. What is the difference between both commands and why do they not work with \middle?

  • Maybe you just want \mid? Though, that won't scale vertically. – morbusg Jul 23 '14 at 16:28
  • I want the middle command to scale vertically like \middle| does. – Marco Breitig Jul 23 '14 at 16:31
  • 2
    See tex.stackexchange.com/q/5502 to get \middle| to behave exactly as \mid – Philippe Goutet Jul 23 '14 at 16:48
  • Thx for hint, I used your suggestion. – Marco Breitig Jul 24 '14 at 7:52

The symbol needs to come after the \middle so


Although redefining primitives always breaks something, somewhere so I would suggest instead


and use \xmiddle (or any other name you wish)

  • Wow thx, that was fast! I tried to play around with a parameter but somehow did not manage to get things right. – Marco Breitig Jul 23 '14 at 16:33
  • Just out of curiosity, do you know how would one do that with a \(U)delcode or \(U)delimiter? (i.e., without \middle?) – morbusg Jul 23 '14 at 16:35
  • 1
    @morbusg \bigm|? – Manuel Jul 23 '14 at 16:45
  • 1
    @morbusg \bigm \Biggm and friends are defined already to be relation just as \bigr is \mathopen – David Carlisle Jul 23 '14 at 16:45
  • 1
    \newcommand{\relmiddle}{\nonscript\;\middle\nonscript\;} – egreg Jul 23 '14 at 17:29

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