314 research outputs found
On the strictness of the quantifier structure hierarchy in first-order logic
We study a natural hierarchy in first-order logic, namely the quantifier
structure hierarchy, which gives a systematic classification of first-order
formulas based on structural quantifier resource. We define a variant of
Ehrenfeucht-Fraisse games that characterizes quantifier classes and use it to
prove that this hierarchy is strict over finite structures, using strategy
compositions. Moreover, we prove that this hierarchy is strict even over
ordered finite structures, which is interesting in the context of descriptive
complexity.Comment: 38 pages, 8 figure
The Power of the Depth of Iteration in Defining Relations by Induction
In this paper we provoke the question of whether the sequence ... is strictly increasing, i.e., the question of whether increasing the depth of iteration increases the expressive power of defining by induction. Solving this question should have a deep impact on computer science as well as on mathematical logic since it is a question in a subject on the crossroads between them, namely, descriptive complexity. We shall mention a potential way of tackling the problem
Algebraic Characterization of the Alternation Hierarchy in FO^2[<] on Finite Words
We give an algebraic characterization of the quantifier alternation hierarchy in first-order two-variable logic on finite words. As a result, we obtain a new proof that this hierarchy is strict. We also show that the first two levels of the hierarchy have decidable membership problems, and conjecture an algebraic decision procedure for the other levels
The Arity Hierarchy in the Polyadic -Calculus
The polyadic mu-calculus is a modal fixpoint logic whose formulas define
relations of nodes rather than just sets in labelled transition systems. It can
express exactly the polynomial-time computable and bisimulation-invariant
queries on finite graphs. In this paper we show a hierarchy result with respect
to expressive power inside the polyadic mu-calculus: for every level of
fixpoint alternation, greater arity of relations gives rise to higher
expressive power. The proof uses a diagonalisation argument.Comment: In Proceedings FICS 2015, arXiv:1509.0282
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