proposition: Lemma unionE f1 f2 : union f1 f2 = to (UM.union (from f1) (from f2)).
proof: Proof. by case: U f1 f2=>x [*]. Qed.
imports: Coq(ssreflect ssrbool ssrfun) mathcomp(ssrnat eqtype seq path bigop) pcm(options prelude finmap seqperm pred seqext) pcm(pcm morphism)