proposition: Lemma dom_map_idemp (x : U) : dom_map (dom_map x : U') = dom_map x :> U''.
proof: Proof. by rewrite /dom_map omap_comp. Qed.
imports: Coq(ssreflect ssrbool ssrfun) mathcomp(ssrnat eqtype seq path bigop) pcm(options prelude finmap seqperm pred seqext) pcm(pcm morphism)