 [Note: The following material is somewhat technical. The reader may wish to casually review it now and return to it as needed, especially in connection with §5. The propositions \(\mathbf{Ref}, \mathbf{LL}, \mathbf{Ref}', \mathbf{LL}', \mathbf{NI}\), and \(\mathbf{ND}\) are identified in the present section and are referred to as such in the rest of the entry.]