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I think the OP means commands that work:

<arg1> \macro <arg2>

to which the answer is "you can't", really. For example, \over isn't exactly infix. Try something like:

{Some text {arg} \over {second} arg}

as see that it applies to everything in the outer group.

Thank you, that's what I need ...

Hi! How do I define infix commands, e.g. \over?