proposition: Lemma inverseUn f1 f2 : valid (f1 \+ f2) -> inverse (f1 \+ f2) = inverse f1 \+ inverse f2.
proof: Proof. move=>W; rewrite /inverse umfoldlUn_frame ?unitR //. by move=>*; rewrite joinAC. Qed.
imports: Coq(ssreflect ssrbool ssrfun) mathcomp(ssrnat eqtype seq path bigop) pcm(options prelude finmap seqperm pred seqext) pcm(pcm morphism)