Can a working factorial function/operator be defined with a syntax like in mathematics? i.e. using the `!` symbol.

I can't think of any use cases of the existing symbol where things could be ambiguous

* ipython `!shell_escape` always has the bang at the start of a line
* something like `0!=1` would be `True` as usual because the other interpretation of `factorial(0) = 1` would be `SyntaxError: can't assign to literal` or similar error)