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arXiv 1803.01552math.LOcs.LO
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直觉命题演算中的不动点消去法(扩展版)

Fixed-point elimination in the Intuitionistic Propositional Calculus (extended version)

Silvio Ghilardi, Maria Joao Gouveia, Luigi Santocanale

摘要:

Heyting代数(即直觉命题演算的代数模型)上的单调多项式的最小和最大不动点总是存在的,即使这些代数不是完全格。原因是这些极值不动点可由IPC的公式定义。因此,基于直觉主义逻辑的$μ$ -演算是平凡的,每个$μ$ -公式等价于一个不动点自由公式。本文给出了公式的最小不动点和最大不动点的公理化,以及计算等价于给定$μ$ -公式的不动点自由公式的算法。最大不动点的公理化是简单的。最小不动点的公理化比较复杂,特别是每一个单调公式通过Kleene迭代在有限步内收敛到它的最小不动点,但迭代次数没有统一的上界。我们从算法中提取出这样的n的上界,这取决于公式的大小。对于某些公式,我们证明了这些上界是多项式的和最优的。

英文摘要:

It is a consequence of existing literature that least and greatest fixed-points of monotone polynomials on Heyting algebras-that is, the alge- braic models of the Intuitionistic Propositional Calculus-always exist, even when these algebras are not complete as lattices. The reason is that these extremal fixed-points are definable by formulas of the IPC. Consequently, the $μ$-calculus based on intuitionistic logic is trivial, every $μ$-formula being equiv- alent to a fixed-point free formula. We give in this paper an axiomatization of least and greatest fixed-points of formulas, and an algorithm to compute a fixed-point free formula equivalent to a given $μ$-formula. The axiomatization of the greatest fixed-point is simple. The axiomatization of the least fixed- point is more complex, in particular every monotone formula converges to its least fixed-point by Kleene's iteration in a finite number of steps, but there is no uniform upper bound on the number of iterations. We extract, out of the algorithm, upper bounds for such n, depending on the size of the formula. For some formulas, we show that these upper bounds are polynomial and optimal.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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