proposition: Lemma mulg_subr A B : 1 \in A -> B \subset A * B.
proof: Proof. by move=> A1; rewrite -{1}(mul1g B) mulSg ?sub1set. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype div path tuple bigop prime finset)