proposition: Lemma zip_sorted' s1 s2 : sorted ord (map key s1) -> forall s, zip' s1 s2 = Some s -> sorted ord (map key s).
proof: Proof. by move=>H s; move/map_key_zip'=>->. Qed.
imports: Coq(ssreflect ssrbool ssrfun) mathcomp(ssrnat eqtype seq path) pcm(options)