fact: Definition swap {A B} (ab : A × B) : B × A := ⟨nsnd ab, nfst ab⟩.
imports: Coq(ssreflect ssrfun ssrbool) Coq(Relation_Definitions Morphisms) Mon(SPropBase SPropMonadicStructures MonadExamples SpecificationMonads DijkstraMonadExamples) Relational(OrderEnrichedCategory OrderEnrichedRelativeMonadExamples)