proposition: Fact hfs_opair_spec a b x y : ⟬a,b⟭ = ⟬x,y⟭ <-> a = x /\ b = y.
proof: Proof. split. + apply hfs_opair_inj. + intros [ [] [] ]; auto. Qed.
imports: List Arith Lia Max Wellfounded Setoid Eqdep_dec Bool Undecidability.Shared.Libs.DLW.Utils(utils_tac utils_list finite) Undecidability.Shared.Libs.DLW.Vec(pos vec) Undecidability.Shared.Libs.DLW.Wf(wf_finite wf_chains) Undecidability.FOL.TRAKHTENBROT(notations fol_ops membership btree)