proposition: Lemma JOIN_fmap_ret : JoinLaws.right_unit (@CRet M N) (@JOIN').
proof: Proof. move=> A. rewrite [JOIN' _]/=. by rewrite JOINE -/prod (Prod.JOIN_fmap_ret prod1 prod3). Qed.
imports: mathcomp(all_ssreflect) HB(structures) monae_lib hierarchy monad_lib