proposition: Lemma quotientSGK A G : A \subset 'N(H) -> H \subset G -> (A / H \subset G / H) = (A \subset G).
proof: Proof. by rewrite -{2}ker_coset; apply: morphimSGK. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq div) mathcomp(choice fintype prime finset fingroup morphism) mathcomp(automorphism)