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arXiv 1406.7684cs.LO
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有界性问题的可判定性结果

Decidability Results for the Boundedness Problem

Achim Blumensath, Martin Otto, Mark Weyer

摘要:

证明了树上基于正一元二阶(MSO)公式的一元最小不动点递归的有界性问题的可判定性。给定一个在X中为正的MSO-公式phi(X,x),可以判定基于phi的不动点递归是否在所有树的类上是伪的,因为对于phi到达其最小不动点所需的迭代次数,在所有树上都是一致的。我们还确定了这个问题的确切复杂性。证明使用自动机理论技术。这一关键结果延伸,通过模型理论的解释,以显示可判定性的有界性问题MSO和保护二阶逻辑(GSO)的类结构的固定有限树宽度。进一步的模型理论转移参数,使我们能够推导出主要的已知的判定性结果的有界性片段的一阶逻辑以及新的。

英文摘要:

We prove decidability of the boundedness problem for monadic least fixed-point recursion based on positive monadic second-order (MSO) formulae over trees. Given an MSO-formula phi(X,x) that is positive in X, it is decidable whether the fixed-point recursion based on phi is spurious over the class of all trees in the sense that there is some uniform finite bound for the number of iterations phi takes to reach its least fixed point, uniformly across all trees. We also identify the exact complexity of this problem. The proof uses automata-theoretic techniques. This key result extends, by means of model-theoretic interpretations, to show decidability of the boundedness problem for MSO and guarded second-order logic (GSO) over the classes of structures of fixed finite tree-width. Further model-theoretic transfer arguments allow us to derive major known decidability results for boundedness for fragments of first-order logic as well as new ones.

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