proposition: Lemma umpreim_undef p : um_preim p undef =1 pred0.
proof: Proof. by move=>x; rewrite /um_preim find_undef. Qed.
imports: Coq(ssreflect ssrbool ssrfun) mathcomp(ssrnat eqtype seq path bigop) pcm(options prelude finmap seqperm pred seqext) pcm(pcm morphism)