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arXiv 2205.09015cs.LO
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自动结构上的Ramsey量词:复杂性及其在验证中的应用

Ramsey Quantifiers over Automatic Structures: Complexity and Applications to Verification

Pascal Bergsträßer, Moses Ganardi, Anthony W. Lin, Georg Zetzsche

摘要:

自动结构是由同步有限状态自动机表示的无限结构。本文关注有限词和树(排名/排名)的自动结构。我们调查的“有向版本”的拉姆齐量词,它表示存在一个无限的有向集团。这包含了拉姆齐量词的标准“无向版本”。首先观察到Ramsey量词与验证中的两个问题之间的有趣联系:(1)规则模型检验中Büchi和广义Büchi条件的可达性可以看作是传递自动图上的Ramsey量化(即,其边关系是传递的),(2)检查一元可分解性(a.k.a.可识别性)可以被看作是在共传递自动图上的Ramsey量化(即,其边关系是传递的补集)。我们提供了一个全面的复杂性景观拉姆齐量词在这三种情况下(一般,传递,共传递),所有NL和EXP之间。反过来,这产生了大量具有精确复杂性的新结果,例如,子树/扁平前缀重写的验证,以及树自动关系上的一元分解。我们还获得了相当简单的证明,例如,对于词自动关系上的一元可分解性的NL复杂度(由DFA给出)。

英文摘要:

Automatic structures are infinite structures that are finitely represented by synchronized finite-state automata. This paper concerns specifically automatic structures over finite words and trees (ranked/unranked). We investigate the "directed version" of Ramsey quantifiers, which express the existence of an infinite directed clique. This subsumes the standard "undirected version" of Ramsey quantifiers. Interesting connections between Ramsey quantifiers and two problems in verification are firstly observed: (1) reachability with Büchi and generalized Büchi conditions in regular model checking can be seen as Ramsey quantification over transitive automatic graphs (i.e., whose edge relations are transitive), (2) checking monadic decomposability (a.k.a. recognizability) of automatic relations can be viewed as Ramsey quantification over co-transitive automatic graphs (i.e., the complements of whose edge relations are transitive). We provide a comprehensive complexity landscape of Ramsey quantifiers in these three cases (general, transitive, co-transitive), all between NL and EXP. In turn, this yields a wealth of new results with precise complexity, e.g., verification of subtree/flat prefix rewriting, as well as monadic decomposability over tree-automatic relations. We also obtain substantially simpler proofs, e.g., for NL complexity for monadic decomposability over word-automatic relations (given by DFAs).

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