proposition: Lemma coset_morphM : {in 'N(A) &, {morph coset : x y / x * y}}.
proof: Proof. move=> x y Nx Ny; apply: val_inj. by rewrite /= !val_coset_prim ?groupM //= rcoset_mul ?nNH. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq div) mathcomp(choice fintype prime finset fingroup morphism) mathcomp(automorphism)