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arXiv 1202.1980cs.LOcs.FLmath.LO
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高阶嵌套下推树上的一阶逻辑

First-Order Logic on Higher-Order Nested Pushdown Trees

Alexander Kartzow

摘要:

我们引入了一个新的层次结构的高阶嵌套下推树推广的Gesar等人。的嵌套下推树概念。嵌套下推树是一种非常有用的控制流表示方法,可以用来验证递归调用一阶函数的程序。高阶嵌套下推树是由高阶下推系统生成的图的展开的扩展。此外,一类嵌套的下推树的水平n是一致的一阶解释的水平n+1的可折叠的下推图类。高阶下推图类和可折叠高阶下推图类之间的关系还不是很清楚。我们希望通过对嵌套下推树层次结构的进一步研究,能够更好地理解这两种层次结构。本文研究了高阶嵌套下推树的一阶模型检验问题。我们表明,一阶模型检验的前两个层次上的层次结构是可判定的。此外,我们还得到了一类一级嵌套下推树的2-EXPSPACE算法。证明技术涉及到一个伪本地分析的策略,在两个相同的副本嵌套下推树的Escherichfeucht-Fraisse游戏。普通的局部性参数在Gaifman引理的精神不适用于这里,因为嵌套的下推树往往有小直径。我们引入了相关祖先的概念,它提供了一个足够的描述的FO_k型的每个元素在一个高阶嵌套下推树。这些祖先的本地分析,使我们能够证明存在的限制性获胜策略的Escherichfeucht-Fraisse游戏。然后,这些策略被用来创建一个一阶模型检验算法。

英文摘要:

We introduce a new hierarchy of higher-order nested pushdown trees generalising Alur et al.'s concept of nested pushdown trees. Nested pushdown trees are useful representations of control flows in the verification of programs with recursive calls of first-order functions. Higher-order nested pushdown trees are expansions of unfoldings of graphs generated by higher-order pushdown systems. Moreover, the class of nested pushdown trees of level n is uniformly first-order interpretable in the class of collapsible pushdown graphs of level n+1. The relationship between the class of higher-order pushdown graphs and the class of collapsible higher-order pushdown graphs is not very well understood. We hope that the further study of the nested pushdown tree hierarchy leads to a better understanding of these two hierarchies. In this paper, we are concerned with the first-order model checking problem on higher-order nested pushdown trees. We show that the first-order model checking on the first two levels of this hierarchy is decidable. Moreover, we obtain an 2-EXPSPACE algorithm for the class of nested pushdown trees of level 1. The proof technique involves a pseudo-local analysis of strategies in the Ehrenfeucht-Fraisse games on two identical copies of a nested pushdown tree. Ordinary locality arguments in the spirit of Gaifman's lemma do not apply here because nested pushdown trees tend to have small diameters. We introduce the notion of relevant ancestors which provide a sufficient description of the FO_k -type of each element in a higher-order nested pushdown tree. The local analysis of these ancestors allows us to prove the existence of restricted winning strategies in the Ehrenfeucht-Fraisse game. These strategies are then used to create a first-order model checking algorithm.

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