proposition: Lemma prod_feta (A B : Type) : @idfun (A * B) = fst \** snd.
proof: Proof. by apply: fext=>x; rewrite /pmorphism -prod_eta. Qed.
imports: Coq(ssreflect ssrbool ssrfun Eqdep) mathcomp(ssrnat seq eqtype choice fintype) pcm(options axioms)