Binary operators

[JLBorges]

> If calling f() first changes the value of h(), or vice versa, then the behavior is undefined.

No. Function calls are indeterminately sequenced; ie. the execution of the function calls are never interleaved. The behaviour is unspecified.

Undefined behaviour: https://eel.is/c++draft/intro.defs#defns.undefined
Unspecified behaviour: https://eel.is/c++draft/intro.defs#defns.unspecified