一句话:证明在有界度结构类上,后继不变一阶逻辑的表达能力不超过普通一阶逻辑。
本文研究后继不变一阶逻辑(successor-invariant FO)的表达能力。该逻辑在一阶逻辑基础上允许使用结构上的一个额外后继关系,但要求公式在有限结构上的有效性不依赖于具体后继关系的选择。作者考察有界度结构类,证明在这一限制下,后继不变一阶逻辑并不比普通一阶逻辑表达更多性质。该结果刻画了辅助后继关系在低度结构上的作用边界,将不变性与一阶表达力联系起来。
We study the expressive power of successor-invariant first-order logic, which is an extension of first-order logic where the usage of an additional successor relation on the structure is allowed, as long as the validity of formulas is independent of the choice of a particular successor on finite structures. We show that when the degree is bounded, successor-invariant first-order logic is no more expressive than first-order logic.