proposition: Lemma unionE f1 f2 : union f1 f2 = to (UM.union (from f1) (from f2)).
proof: Proof. by []. Qed.
imports: Coq(ssreflect ssrbool ssrfun) mathcomp(ssrnat eqtype seq path interval) pcm(options prelude pred finmap rtc seqext useqord uslice uconsec)