proposition: Lemma quotient_cprod : K \* H = G -> (K / M) \* (H / M) = G / M.
proof: Proof. exact: morphim_cprod. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq div) mathcomp(choice fintype bigop finset fingroup morphism) mathcomp(quotient action)