std::equivalence_relation

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Comparison concepts
equality_comparableequality_comparable_with (C++20)(C++20)
totally_orderedtotally_ordered_with (C++20)(C++20)
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invocableregular_invocable (C++20)(C++20)
predicate (C++20)
relation (C++20)
equivalence_relation (C++20)
strict_weak_order (C++20)

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boolean-testable (C++20)

Defined in header`<concepts>`
template<class R,class T,class U> concept equivalence_relation=std::relation<R, T, U>;		(since C++20)

The conceptequivalence_relation<R, T, U> specifies that therelationR imposes anequivalence relation on its arguments.

A relationr is an equivalence relation if

it is reflexive: for allx,r(x, x) istrue;
it is symmetric: for alla andb,r(a, b) istrue if and only ifr(b, a) istrue;
it is transitive:r(a, b) && r(b, c) impliesr(a, c).