proposition: Fact hfs_pair_spec r s x : x ∈ hfs_pair r s <-> x = r \/ x = s.
proof: Proof. unfold hfs_pair. do 2 rewrite hfs_cons_spec. rewrite hfs_empty_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)