fact: Definition Σ2_is_opair p x y := ∃∃ Σ2_is_pair 1 (2+x) (2+x) ⟑ Σ2_is_pair 0 (2+x) (2+y) ⟑ Σ2_is_pair (2+p) 1 0.
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)