proposition: Lemma umall20 : um_all2 Unit Unit.
proof: Proof. by move=>k; rewrite /optionR /= find0E. Qed.
imports: Coq(ssreflect ssrbool ssrfun) mathcomp(ssrnat eqtype seq path bigop) pcm(options prelude finmap seqperm pred seqext) pcm(pcm morphism)