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