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I write a lot |, for instance, even numbers = \{ z | z \in Z, z mod 2 = 0 \}. But the space around | does not look enough... I tried \mathbin{|} and \quad | \quad, they do not look great either...

Could anyone tell me a conventional way to put space around |?

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How about \mid? –  Werner Nov 14 '11 at 9:26
You should write z \equiv 0 \pmod{2} or z \bmod 2 = 0. –  Andrey Vihrov Nov 14 '11 at 9:27
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1 Answer 1

up vote 5 down vote accepted

Actually you were on the right track, but it's \mathrel{|}, for which LaTeX has the abbreviation \mid.

The formula should be more correctly written as

\{\, z \mid z\in Z, z \bmod 2 = 0 \,\}
\{\, z \mid z\in Z, z \equiv 0 \pmod{2} \,\}
\{\, z\in Z \mid z \bmod 2 = 0 \,\}
\{\, z\in Z \mid z \equiv 0 \pmod{2} \,\}

Take your pick. If you write something like "even numbers = {z ...}" (which I don't like, preferring to say "the even numbers are those in the set {z ...}"), put the equals sign inside the formula

even numbers~\(=\{\, ... \,\}

or, if the text is already inside math mode (in an alignment, for instance), use

\text{even numbers} = \{\, ... \,\}

Note that \text is provided by the amsmath package.

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I wonder if there is a semantically better way to typeset set definitions, as \, does not appeal to me. –  Andrey Vihrov Nov 14 '11 at 10:08
@AndreyVihrov The \, is a matter of personal taste. One way to avoid it might be to define \lset and \rset to be respectively \{\, and \,\}. Or directly redefining \{ provided it's not used elsewhere: \renewcommand\{{\lbrace\,} and similarly for \} with \rbrace. –  egreg Nov 14 '11 at 10:14
The braket package provides the commands \set (online math mode) and \Set (display math mode) to fill just this need. –  Mico Nov 14 '11 at 11:07
@Mico It's disputable if this is really an improvement. :) –  egreg Nov 14 '11 at 11:25
@egreg: I'm with you -- I just insert the spacing commands to the right of the opening curly and to the left of the closing curly brace by hand; remembering the syntax of \set{... is too cumbersome, given the relatively low frequency of needing to use it arises in my work. –  Mico Nov 14 '11 at 11:40
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