proposition: Lemma omf_unit f : f Unit = Unit.
proof: Proof. by case: f=>s [m H] /=; rewrite H omap0. Qed.
imports: Coq(ssreflect ssrbool ssrfun) mathcomp(ssrnat eqtype seq path bigop) pcm(options prelude finmap seqperm pred seqext) pcm(pcm morphism)