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arXiv 2101.05754cs.LO
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经典项演算的一种强互模拟

A Strong Bisimulation for a Classical Term Calculus

Eduardo Bonelli, Delia Kesner, Andrés Viso

AI总结:

本文通过引入修订的 λμ-演算 ΛM 和关系 ≃,解决了 Laurent 的 ≃σ-等价在经典项演算中无法构成强互模拟的问题,并证明 ≃ 是 ΛM 归约下的强互模拟。

摘要:

当把一个项演算翻译成图形形式体系时,许多非本质细节会被抽象掉。在将 λ-演算翻译为证明网的情形中,这些非本质细节由 λ-项上一种称为 ≃σ-等价的等价概念来刻画,这既适用于直觉主义情形(归功于 Regnier),也适用于经典情形(归功于 Laurent)。本文的目的是揭示 ≃σ-等价背后的一种强互模拟,该等价由 Laurent 针对 Parigot 的 λμ-演算所表述。为此,我们引入一个关系 ≃,它定义在我们称为 ΛM 的 λμ-演算修订表示之上。更准确地说,我们首先找出 Laurent 在 λμ-项上的 ≃σ-等价未能成为强互模拟的原因。受 Laurent 的极化证明网启发,这引导我们区分项上的乘法归约步骤和指数归约步骤。其次,我们丰富 λμ 的语法,使我们能够追踪指数运算。这些技术要素为经典情形下的强互模拟铺平了道路。我们引入一个演算 ΛM 和一个关系 ≃,并证明它关于 ΛM 中的归约是一个强互模拟,即两个 ≃-等价项具有完全相同的归约语义,这一结果在 λ-演算中 Regnier 的 ≃σ-等价以及在 λμ 中 Laurent 的 ≃σ-等价上都不成立。尽管 ≃ 是在一个丰富语法上表述的,因此并不严格包含在 Laurent 的 ≃σ 中,但我们展示了如何将它视为对 Laurent ≃σ 的一种限制。

英文摘要:

When translating a term calculus into a graphical formalism many inessential details are abstracted away. In the case of $λ$-calculus translated to proof-nets, these inessential details are captured by a notion of equivalence on $λ$-terms known as $\simeq_σ$-equivalence, in both the intuitionistic (due to Regnier) and classical (due to Laurent) cases. The purpose of this paper is to uncover a strong bisimulation behind $\simeq_σ$-equivalence, as formulated by Laurent for Parigot's $λμ$-calculus. This is achieved by introducing a relation $\simeq$, defined over a revised presentation of $λμ$-calculus we dub $ΛM$. More precisely, we first identify the reasons behind Laurent's $\simeq_σ$-equivalence on $λμ$-terms failing to be a strong bisimulation. Inspired by Laurent's \emph{Polarized Proof-Nets}, this leads us to distinguish multiplicative and exponential reduction steps on terms. Second, we enrich the syntax of $λμ$ to allow us to track the exponential operations. These technical ingredients pave the way towards a strong bisimulation for the classical case. We introduce a calculus $ΛM$ and a relation $\simeq$ that we show to be a strong bisimulation with respect to reduction in $ΛM$, ie. two $\simeq$-equivalent terms have the exact same reduction semantics, a result which fails for Regnier's $\simeq_σ$-equivalence in $λ$-calculus as well as for Laurent's $\simeq_σ$-equivalence in $λμ$. Although $\simeq$ is formulated over an enriched syntax and hence is not strictly included in Laurent's $\simeq_σ$, we show how it can be seen as a restriction of it.

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