proposition: Lemma lastkeyfUn A (h1 h2 : natmap A) : valid (h1 \+ h2) -> last_key h1 <= last_key (h1 \+ h2).
proof: Proof. by move=>X; apply: lastkey_mono=>x; rewrite domUn inE X => ->. Qed.
imports: Coq(ssreflect ssrbool ssrfun) mathcomp(ssrnat eqtype seq path interval) pcm(options prelude pred finmap rtc seqext useqord uslice uconsec)