一句话:证明了模糊一阶逻辑中相对于双模拟距离非扩张的公式恰可由模糊模态公式逼近。
van Benthem 定理经典地刻画了命题模态逻辑是一阶逻辑中双模拟不变的片段。本文将其推广到模糊(定量)情形:在一阶模糊谓词逻辑及其模态片段上,引入自然的双模拟距离概念。主要结果是,模糊一阶公式若相对于该双模拟距离是非扩张的,则恰好是那些能被模糊模态公式逼近的公式。由此给出了模糊模态逻辑的模型论刻画,把经典的双模拟不变性结果提升到定量语义框架,为模糊/定量模态逻辑的表达力提供了统一解释。
We present a fuzzy (or quantitative) version of the van Benthem theorem, which characterizes propositional modal logic as the bisimulation-invariant fragment of first-order logic. Specifically, we consider a first-order fuzzy predicate logic along with its modal fragment, and show that the fuzzy first-order formulas that are non-expansive w.r.t. the natural notion of bisimulation distance are exactly those that can be approximated by fuzzy modal formulas.