proposition: Lemma cosetpreK C : coset H @*^-1 C / H = C.
proof: Proof. by rewrite /quotient morphpreK ?sub_im_coset. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq div) mathcomp(choice fintype prime finset fingroup morphism) mathcomp(automorphism)