Distance to semicolon in math mode

Question

When using colon (:) in math mode, it always appears equidistant from the objects on either side of it.

Observe this e.g. when typesetting $(a:b)$.

If one instead uses $(a \colon b)$, the colon is closer to the a, as it would be in ordinary writing.

On the other hand, if one typesets $(a;b)$, one finds that the semicolon is not equidistant between a and b, but closer to the a, as with the \colon command above.

So my question is: Is there a command that creates a semicolon equidistant from the objects to either side of it, as with the :?

Answer 1

LaTeX inherits a set of plain TeX commands that let you change the "class" of each character in math mode. The various classes determine how the TeX engine inserts white space in a formula.

There are 8 classes:

• 0 = Ordinary \
• 1 = Large operator \sum
• 2 = Binary operator +
• 3 = Relation =
• 4 = Opening (
• 5 = Closing )
• 6 = Punctuation ,
• 7 = Variable

I think ; is punctuation by default, but you can make it behave like a binary operator with \mathbin{;} or like a relation with \mathrel{;}.

The corresponding commands for the first 7 classes are: \mathord, \mathop, \mathbin, \mathrel, \mathopen, \mathclose, and \mathpunct.

See the TexBook, p.155 for more.