proposition: Lemma omap_undef a : omap a undef = undef.
proof: Proof. by rewrite /omap valid_undef. Qed.
imports: Coq(ssreflect ssrbool ssrfun) mathcomp(ssrnat eqtype seq path bigop) pcm(options prelude finmap seqperm pred seqext) pcm(pcm morphism)