is_ass.
AddnilL;eapply weakening;apply Nc_AxiomH;assumption.
mp;eassumption.
Qed.
(** Nc to Hc *)

(* Specifications: *)
Lemma H_weakening : forall Γ Δ A, (forall B, In B Γ -> In B Δ) -> Γ ⊢H A -> Δ ⊢H A.
induction 2.