A non-preferential semantics of non-monotonic modal logic (Q1028644)

In modal logics with a connective for negative introspection, expansions are usually defined as the fixpoints of a suitable operation. An exception is due to G. Schwartz, who in 1992 devised a semantics for such logics in which the expansions of a set of formulae are taken to be the theories of models of that set that are minimal under a suitable preference relation. In the paper under review, the author constructs another non-fixpoint semantics, but without preference relations. In it, the expansions of a set of formulae are taken to be the theories of `isolated clusters' of canonical models of that set.