14.9.5 Enumeration comparison operators

Every enumeration type implicitly provides the following predefined
comparison operators:
bool operator ==(E x, E y);
bool operator !=(E x, E y);
bool operator <(E x, E y);
bool operator >(E x, E y);
bool operator <=(E x, E y);
bool operator >=(E x, E y);
The result of evaluating x op y, where x and y are expressions of an
enumeration type E with an underlying
type U, and op is one of the comparison operators, is exactly the same as
evaluating ((U)x) op ((U)y). In
other words, the enumeration type comparison operators simply compare the
underlying integral values of
the two operands.