proposition: Lemma freeUnR k f1 f2 : k \notin dom f2 -> free (f1 \+ f2) k = free f1 k \+ f2.
proof: Proof. by move=>H; rewrite joinC freeUnL // joinC. Qed.
imports: Coq(ssreflect ssrbool ssrfun) mathcomp(ssrnat eqtype seq path bigop) pcm(options prelude finmap seqperm pred seqext) pcm(pcm morphism)