proposition: Fact hfs_incl_ext s t : s = t <-> s ⊆ t /\ t ⊆ s.
proof: Proof. split. + intros []; auto. + rewrite hfs_mem_ext; intros []; split; auto. 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)