TeX-like "def" macro doesn't allow inverting the arguments order (a.k.a. "overset" not supported)

[Omikhleia]

Formula:

\def{overset}{\munderover{#2}{}{#1}}
R^n \overset{A}{→} R^m

This issue should have been a proposal: "Let's support TeX-like \overset which is a nice convenience"... and here would have been expected to produce the arrow with a smaller A on top of it... and surely a simple macro is enough, right?

... But the above crashes with "Wrong number of arguments (2) for command overset (should be 1)"

Extra test: as in the code, fractions are defined as \def{frac}{\mfrac{#2}{#1}} and \frac{x}{y} gives x / y...
Let's try \def{invfrac}{\mfrac{#2}{#1}} and expecting it to be produce y / x...
Same failure as above.

So we have these def-macro thing "to save (us) some typing"...
How can we achieve \overset? "When macros are not enough, creating new mathematical elements is quite simple" (... followed by lots of not-so-simple explanation for a newcomer). Sure. It's typically a case where a macro would have been neat, though.

🌵 My dear math friends, yes, again... Will you start to typeset some real maths one day? Just askin'

Subsidiary remark: Nowhere does the documentation says how little of the TeX-like math syntax¹ is currently supported... and if there are any real goals in making it more complete.... But the reality check leads to serious doubts... 😬

Footnotes

1. Read "commands". But you got the point. ↩

[Omikhleia]

To make it clear, the goal here would be to support TeX math \overset and \underset (and possibly too \stackrel)

Subsidiary question: How to have them considered as relations.

Additional reference:

https://github.com/jgm/texmath/blob/4315006320ea7119fb1c1a1ca5aaf755b0a2bff7/src/Text/TeXMath/Readers/TeX.hs#L745-L755