[Tex/LaTex] What does `\mathrel{}` do (with the empty parameter group)


I know basically what \mathrel does when it's given a parameter: it typesets its parameter as though it were a mathematical relation for the purposes of spacing.

However, I have seen in several places the usage \mathrel{}, which seems to be treating the empty group as a relation.
This doesn't square with how I've been told \mathrel is supposed to work; is there something else going on here?

In short, what does \mathrel (and, presumably, \mathbin, \mathop, etc.) do when its parameter is an empty group?

(I have seen this other question, but it didn't make sense to me and seemed to be not quite the same as mine.)

Best Answer

In math mode {} makes an empty math atom (not just an empty group as in text mode) so \mathrel{} makes an empty atom that gets relation spacing.


$a {} b$ to $ a \mathrel{} b$

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