proposition: Fact pos_dec_reif n (P : pos n -> Prop) (HP : forall p, { P p } + { ~ P p }) : ex P -> sig P.
proof: Proof. apply finite_t_dec_choose_one; auto. Qed.
imports: List Arith Lia Undecidability.Shared.Libs.DLW.Utils(utils_tac utils_list utils_nat fin_base) Undecidability.Shared.Libs.DLW.Vec(pos vec)