proposition: Lemma unitb_undef : unitb (undef : U) = false.
proof: Proof. by case: unitbP =>// /undef0. Qed.
imports: Coq(ssreflect ssrbool ssrfun) mathcomp(ssrnat eqtype seq bigop fintype finset) pcm(options axioms prelude seqperm pred seqext)