(** Weakening *)

(* Specifications: *)
Theorem gen_weakening {s : nd} {b : logic} A phi :
A ⊢ phi -> forall rho B, A <<= B -> ren_ctx rho B ⊢ ren rho phi.
Corollary Weak {s : nd} {b : logic} A B phi :
A ⊢ phi -> A <<= B -> B ⊢ phi.