proposition: Lemma osub_transitive: forall o1 o2 o3, osub o1 o2 -> osub o2 o3 -> osub o1 o3.
proof: Proof. unfold osub. intros ? ? ? hs1 hs2 a3 h3. generalize (hs2 _ h3); intros [ a2 [ h2 ? ]]. generalize (hs1 _ h2); intros [ a1 [ h1 ? ]]. eauto. Qed.
imports: List Dblib(DblibTactics DeBruijn)