proposition: Lemma subdomF k f : {subset dom (free f k) <= dom f}.
proof: Proof. by move=>x; rewrite domF inE; case: eqP. Qed.
imports: Coq(ssreflect ssrbool ssrfun) mathcomp(ssrnat eqtype seq path bigop) pcm(options prelude finmap seqperm pred seqext) pcm(pcm morphism)