 Dunn put forward his semantics to characterize the logic of First Degree Entailment (FDE), which treats only entailments between implication-free formulas. (For papers on the nature and development of FDE, see Omori &amp; Wansing 2017.) Richard Routley (1988) extended the theory to treat some weak relevant logics, and Restall (1995) extended the theory to treat logics just weaker than the promenant relevant logics E and R (see sections 4 and 5 below). Mares (2004a) used a neighbourhood semantics, together with four truth-values to give a semantics for R. The four-valued semantics is treated in more detail the entry on paraconsistent logics. Other treatments of negation, some of which have been used for relevance logics, can be found in Wansing (2001) and in the entry on negation.