proposition: Lemma undefbE f : f = undef <-> undefb f.
proof: Proof. by case: undefbP. Qed.
imports: Coq(ssreflect ssrbool ssrfun) mathcomp(ssrnat eqtype seq path bigop) pcm(options prelude finmap seqperm pred seqext) pcm(pcm morphism)