proposition: Fact hfs_mem_dec : forall s t, { s ∈ t } + { ~ s ∈ t }.
proof: Proof. intros (s & ?) (t & ?); simpl; apply btm_dec. Qed.
imports: List Arith Lia Max Wellfounded Setoid Eqdep_dec Bool Undecidability.Shared.Libs.DLW.Utils(utils_tac utils_list finite) Undecidability.Shared.Libs.DLW.Vec(pos vec) Undecidability.Shared.Libs.DLW.Wf(wf_finite wf_chains) Undecidability.FOL.TRAKHTENBROT(notations fol_ops membership btree)