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arXiv math/0405326math.LO
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没有量词替换的定义

Definitions with no quantifier alternation

Oleg Pikhurko, Joel Spencer, Oleg Verbitsky

摘要:

令$D(G)$是定义图$G$直到同构的一阶句子$Φ$的最小量词深度。假设$D_0(G)$是$D(G)$的版本,其中我们不允许在$Φ$中替换量词。定义$q_0(n)$为$n$阶的所有图$G$上的$D_0(G)$的最小值。我们证明,对于所有的$n$,我们有$\log^*n-\log^*\log^*n-1\le q_0(n)\le \log^*n+22$,其中$\log^*n$等于最小的迭代次数的二进制对数需要使$n$为1或以下。通过构造具有极小深度的模分解的特殊图,得到了其上界。

英文摘要:

Let $D(G)$ be the minimum quantifier depth of a first order sentence $Φ$ that defines a graph $G$ up to isomorphism. Let $D_0(G)$ be the version of $D(G)$ where we do not allow quantifier alternations in $Φ$. Define $q_0(n)$ to be the minimum of $D_0(G)$ over all graphs $G$ of order $n$. We prove that for all $n$ we have $\log^*n-\log^*\log^*n-1\le q_0(n)\le \log^*n+22$, where $\log^*n$ is equal to the minimum number of iterations of the binary logarithm needed to bring $n$ to 1 or below. The upper bound is obtained by constructing special graphs with modular decomposition of very small depth.

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