proposition: Lemma findUnR k f1 f2 : valid (f1 \+ f2) -> find k (f1 \+ f2) = if k \in dom f2 then find k f2 else find k f1.
proof: Proof. by rewrite joinC=>D; rewrite findUnL. Qed.
imports: Coq(ssreflect ssrbool ssrfun) mathcomp(ssrnat eqtype seq path bigop) pcm(options prelude finmap seqperm pred seqext) pcm(pcm morphism)