proposition: Lemma lastkey_undef A : last_key (undef : natmap A) = 0.
proof: Proof. by rewrite /last_key /undef /= !umEX. Qed.
imports: Coq(ssreflect ssrbool ssrfun) mathcomp(ssrnat eqtype seq path interval) pcm(options prelude pred finmap rtc seqext useqord uslice uconsec)