proposition: Lemma joing_subP A B G : reflect (A \subset G /\ B \subset G) (A <*> B \subset G).
proof: Proof. by rewrite join_subG; apply: andP. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype div path tuple bigop prime finset)