proposition: Lemma xcprodmEr : {in K, forall y, xcprodm (cpair1g y) = fK y}.
proof: Proof. by move=> y Ky; rewrite /xcprodm cprodmEr ?mem_morphim ?ifactmE. Qed.
imports: mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq div) mathcomp(fintype bigop finset fingroup morphism perm) mathcomp(automorphism quotient action gproduct gfunctor) mathcomp(cyclic)