proposition: Lemma cprod_card_dprod G A B : A \* B = G -> #|A| * #|B| <= #|G| -> A \x B = G.
proof: Proof. by case/cprodP=> [[K H -> ->] <- cKH] /cardMg_TI; apply: dprodE. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq div) mathcomp(choice fintype bigop finset fingroup morphism) mathcomp(quotient action)