proposition: Lemma dprodWsdC A B G : A \x B = G -> B ><| A = G.
proof: Proof. by rewrite dprodC => /dprodWsd. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq div) mathcomp(choice fintype bigop finset fingroup morphism) mathcomp(quotient action)