proposition: Lemma umfoldr0 a z0 d : um_foldr a z0 d Unit = z0.
proof: Proof. by rewrite /um_foldr assocs0 valid_unit. Qed.
imports: Coq(ssreflect ssrbool ssrfun) mathcomp(ssrnat eqtype seq path bigop) pcm(options prelude finmap seqperm pred seqext) pcm(pcm morphism)