Defined in header
template<class F, class I1, class I2 = I1>
concept indirect_equivalence_relation =
indirect_equivalence_relation specifies requirements for algorithms that call equivalence relations as their arguments. The key difference between this concept and std::equivalence_relation is that it is applied to the types that
I2 references, rather than
 Semantic requirements
indirect_equivalence_relation only if all concepts it subsumes are modeled.