Bounded-Arity Hierarchies in Fixed-Point Logics
نویسنده
چکیده
In this paper we prove that for each k, the expressive power of k–ary fixed–point logic, i.e. the fragment of fixed–point logic whose fixed–point operators are restricted to arity ≤ k, strictly exceeds the power of (k − 1)–ary fixed–point logic. This solves a problem that was posed by Chandra and Harel in 1982. Our proof has a rather general form that applies to several variants of fixed–point logic and also to transitive–closure logic.
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