proposition: Lemma commSg A B C : A \subset B -> [~: A, C] \subset [~: B, C].
proof: Proof. by move=> sAC; rewrite genS ?imset2S. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype div path tuple bigop prime finset)