proposition: Lemma quotientJ A x : x \in 'N(H) -> A :^ x / H = (A / H) :^ coset H x.
proof: Proof. exact: morphimJ. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq div) mathcomp(choice fintype prime finset fingroup morphism) mathcomp(automorphism)