proposition: Lemma In0 x : x \In (Unit : U) -> False.
proof: Proof. by case=>_; case=>z /esym/unitbP; rewrite um_unitbPtUn. Qed.
imports: Coq(ssreflect ssrbool ssrfun) mathcomp(ssrnat eqtype seq path bigop) pcm(options prelude finmap seqperm pred seqext) pcm(pcm morphism)