proposition: Lemma uvalid_undef_fin : ~~ valid uundef.
proof: Proof. by apply/negP=>/forallP/(_ i); rewrite sel_fin valid_undef. Qed.
imports: Coq(ssreflect ssrbool ssrfun) mathcomp(ssrnat eqtype seq bigop fintype finset) pcm(options axioms prelude seqperm pred seqext)