proposition: Fact hfs_pair_spec' p r s : p = hfs_pair r s <-> (forall x, x ∈ p <-> x = r \/ x = s).
proof: Proof. rewrite hfs_mem_ext. fol equiv; intro. rewrite hfs_pair_spec; tauto. 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)