proposition: Lemma umpreim_pred0 f : um_preim pred0 f =1 pred0.
proof: Proof. by move=>x; rewrite /um_preim; by case: (find x f). Qed.
imports: Coq(ssreflect ssrbool ssrfun) mathcomp(ssrnat eqtype seq path bigop) pcm(options prelude finmap seqperm pred seqext) pcm(pcm morphism)