proposition: Lemma uvalidU_fin : uvalid uunit.
proof: Proof. by apply/forallP=>t; rewrite sel_fin valid_unit. Qed.
imports: Coq(ssreflect ssrbool ssrfun) mathcomp(ssrnat eqtype seq bigop fintype finset) pcm(options axioms prelude seqperm pred seqext)