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