fact: Definition mb_is_opair p x y := exists a b, a ≋ ⦃x,x⦄ /\ b ≋ ⦃x,y⦄ /\ p ≋ ⦃a,b⦄.
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)