proposition: Lemma lastval_undef : last_val um_undef = None.
proof: Proof. by rewrite /last_val lastkey_undef find_undef. Qed.
imports: Coq(ssreflect ssrbool ssrfun) mathcomp(ssrnat eqtype seq path interval) pcm(options prelude pred finmap rtc seqext useqord uslice uconsec)