proposition: Lemma find0E k : find k (Unit : U) = None.
proof: Proof. by rewrite pcmE /= !umEX /UM.find /= fnd_empty. Qed.
imports: Coq(ssreflect ssrbool ssrfun) mathcomp(ssrnat eqtype seq path bigop) pcm(options prelude finmap seqperm pred seqext) pcm(pcm morphism)