 The semantics that is presented here is the ternary relation semantics due to Richard Routley and Robert K. Meyer. This semantics is a development of Alasdair Urquhart’s “semilattice semantics” (Urquhart 1972). There is a similar semantics, due to Kit Fine, that was developed at the same time as the Routley-Meyer theory (Fine 1974). And there is an algebraic semantics due to J. Michael Dunn. Urquhart’s, Fine’s, and Dunn’s models are very interesting in their own right, but we do not have room to discuss them here.