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