proposition: Lemma valid_unit : valid (@Unit U).
proof: Proof. rewrite /valid/Unit. by case: U=>tp [v j z Cj Aj Uj Vm Vu *]. Qed.
imports: Coq(ssreflect ssrbool ssrfun) mathcomp(ssrnat eqtype seq bigop fintype finset) pcm(options axioms prelude seqperm pred seqext)