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arXiv 1012.3372cs.LO
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纯类型系统证明搜索的聚焦序列演算框架

A Focused Sequent Calculus Framework for Proof Search in Pure Type Systems

Stéphane Jean Eric Lengrand, Roy Dyckhoff, James McKinna

摘要:

逻辑学和类型论中的基本证明搜索策略可以被看作是规则在适当的微积分中的根优先应用,最好没有由规则置换产生的冗余。本文讨论的问题,定义这样的纯类型系统(PTS,这是最初提出的自然演绎风格),然后组织他们的规则,有效的证明搜索。我们引入纯类型序列演算与元变量(PTSCalpha)的想法,通过丰富的语法的置换自由演算的命题逻辑由于Herbelin,这是密切相关的自然演绎和已经很好地适应证明搜索。的操作语义是改编自Herbelin的,并定义了一个系统的本地重写规则,在削减消除,使用明确的替代。我们证明了这个系统的融合。限制我们的注意力PTSC,这个系统的地面条款的类型系统,我们得到的主题约简属性,并表明每个PTSC是逻辑等价于其相应的PTS,前者是强正规化的当且仅当后者是。我们展示了如何使PTSC的逻辑规则到一个语法导向的系统PS证明搜索,通过将转换规则的类型检查的PTS规则的语法导向的演示文稿。最后,我们考虑如何使用PTSCalpha的显式作用域元变量来表示部分证明项,并使用它们来分析交互式证明构造。这建立了一个框架PE,我们能够研究证明搜索策略,类型居民枚举和(高阶)统一。

英文摘要:

Basic proof-search tactics in logic and type theory can be seen as the root-first applications of rules in an appropriate sequent calculus, preferably without the redundancies generated by permutation of rules. This paper addresses the issues of defining such sequent calculi for Pure Type Systems (PTS, which were originally presented in natural deduction style) and then organizing their rules for effective proof-search. We introduce the idea of Pure Type Sequent Calculus with meta-variables (PTSCalpha), by enriching the syntax of a permutation-free sequent calculus for propositional logic due to Herbelin, which is strongly related to natural deduction and already well adapted to proof-search. The operational semantics is adapted from Herbelin's and is defined by a system of local rewrite rules as in cut-elimination, using explicit substitutions. We prove confluence for this system. Restricting our attention to PTSC, a type system for the ground terms of this system, we obtain the Subject Reduction property and show that each PTSC is logically equivalent to its corresponding PTS, and the former is strongly normalising iff the latter is. We show how to make the logical rules of PTSC into a syntax-directed system PS for proof-search, by incorporating the conversion rules as in syntax-directed presentations of the PTS rules for type-checking. Finally, we consider how to use the explicitly scoped meta-variables of PTSCalpha to represent partial proof-terms, and use them to analyse interactive proof construction. This sets up a framework PE in which we are able to study proof-search strategies, type inhabitant enumeration and (higher-order) unification.

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