fact: Definition mb_is_pair p x y := forall a, a ∈ p <-> a ≈ x \/ a ≈ y.
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)