proposition: Lemma wf_unproj21 : forall (R:binary A1), wf R -> wf (unproj21 A2 R).
proof: Proof. Proof using. intros R H [x1 x2]. gen x2. induction_wf IH: H x1. constructor. intros [y1 y2]. auto. Qed.
imports: TLC(LibTactics LibLogic LibProd LibSum LibRelation LibNat LibInt)