このへん?
13.6 Overloading
12 For every pair of promoted arithmetic types L and R, there exist candidate operator functions of the form
LR operator*(L, R);
LR operator/(L, R);
LR operator+(L, R);
LR operator-(L, R);
bool operator<(L, R);
bool operator>(L, R);
bool operator<=(L, R);
bool operator>=(L, R);
bool operator==(L, R);
bool operator!=(L, R);
where LR is the result of the usual arithmetic conversions between types L and R.