here's something you should always remember. It will save you some time debugging

COMPARATORS MUST RETURN FALSE IF BOTH ARE EQUAL

although it may not seem logical at first, custom-made comparators MUST return false, if a == b, because they must follow a strict weak ordering

One of the properties of the strict weak ordering is the following: Nothing is considered less than itself. That means that:

if (a > b) return True
if (a == b) return False
if (a < b) return False

If you'll somehow forget about it, there are always std::greater<> and std::less<> waiting for you to use them

Others include

• std::less_equal<>

• std::greater_equal<>

• std::equal_to<>

• std::not_equal_to<>