< cpp‎ | concepts
Defined in header <concepts>
template <class R, class T, class U>

concept Relation =
  std::Predicate<R, T, T> && std::Predicate<R, U, U> &&

  std::Predicate<R, T, U> && std::Predicate<R, U, T>;
(1) (since C++20)

The concept Relation<R, T, U> specifies that R defines a binary relation over the set of expressions whose type and value category are those encoded by either T or U.