proposition: Lemma cpair1g_dom : K \subset 'dom (in_cprod \o @pair1g gTH gTK).
proof: Proof. by rewrite -sub_morphim_pre ?subsetT // morphim_pair1g setXS ?sub1G. 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)