The type must work with < operator and the result should have standard semantics.
c, expressions of type
The following expressions must be valid and have their specified effects.
| || implicitly convertible to || Establishes strict weak ordering relation with the following properties
To satisfy this requirement, types that do not have built-in comparison operators have to provide a user-defined operator<
For the types that are both
LessThanComparable, the C++ standard library makes a distinction between equality, which is the value of the expression
a == b and equivalence, which is the value of the expression
!(a < b) && !(b < a).
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