proposition: Lemma domUnE f1 f2 x : valid (f1 \+ f2) -> x \in dom (f1 \+ f2) = (x \in dom f1) || (x \in dom f2).
proof: Proof. by move=>W; rewrite domUn inE W. Qed.
imports: Coq(ssreflect ssrbool ssrfun) mathcomp(ssrnat eqtype seq path bigop) pcm(options prelude finmap seqperm pred seqext) pcm(pcm morphism)