Cut-Down Operations on Bilattices

In this paper, Melvin Fitting\´s notion of a "cut-down" operation on a bilattice is considered. It is shown that the logic of cut-down operations on bilattices is equivalent to Harry Deutsch\´s four-valued S_fde, demonstrating that S_fde is as intimately connected to the theory of bilattices as is the Dunn-Belnap logic E_fde. The paper concludes by observing that the "not ¬" operation of Carlos Damásio and Luís Pereira serves as a cut-down in Fitting\´s sense and that the logic of Damásio-Pereira cut-down operations on the bilattice NINE is equivalent to Richard Angell\´s AC.