22 Iterators library [iterators]

22.3 Iterator requirements [iterator.requirements]

22.3.7 Common algorithm requirements [alg.req]

22.3.7.8 Concept Sortable [alg.req.sortable]

The Sortable concept specifies the common requirements of algorithms that permute sequences into ordered sequences (e.g., sort).
template<class I, class R = ranges::less<>, class P = identity>
  concept Sortable =
    Permutable<I> &&
    IndirectStrictWeakOrder<R, projected<I, P>>;