proposition: Fact Σ2_is_opair_vars p x y : fol_vars (Σ2_is_opair p x y) ⊑ p::x::y::nil.
proof: Proof. cbv; tauto. Qed.
imports: List Arith Nat Lia Max Wellfounded Coq.Setoids.Setoid Undecidability.Shared.Libs.DLW.Utils(utils_tac utils_list finite) Undecidability.Shared.Libs.DLW.Vec(pos vec) Undecidability.FOL.TRAKHTENBROT(notations fol_ops fo_sig fo_terms fo_logic)