proposition: Lemma quotientMidr A : A * H / H = A / H.
proof: Proof. by rewrite [_ /_]morphimMr ?normG //= -!quotientE trivg_quotient mulg1. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq div) mathcomp(choice fintype prime finset fingroup morphism) mathcomp(automorphism)