A Skeptical Semantics for Truth Maintenance

To generalize the 2-valued stable model semantics for truth maintenance, we introduce a 3-valued stable model semantics. Unlike the 2-valued semantics, this semantics can be given compositional properties. In particular we show that a canonical model (the skeptical model) can be derived as a composition of 3-valued interpretations. The skeptical model can also be characterized by a fixpoint construction. We show that using this construction, the skeptical model can be computed in O(n2).