Why is inequality tested as (!(a==b)) in a lot of C++ standard library code?

Question

This is the code from the C++ standard library remove code. Why is inequality tested as if (!(*first == val)) instead of if (*first != val)

Answer 1

The EqualityComparable concept only requires that operator== be defined.

Consequently, any function that professes to work with types satisfying EqualityComparable cannot rely on the existence of operator!= for objects of that type. (unless there are additional requirements that imply the existence of operator!=).