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