一句话:证明宽度为一的有限关系结构在 ZF 中紧致,否则其紧致性蕴含 3 维空间存在不可测集。
论文研究有限关系结构 A 的紧致性:若对任意同类型无限关系结构 B,B 到 A 的同态存在当且仅当其所有有限子结构到 A 的同态存在,则称 A 紧致。作者考察这一性质在集合论公理系统中的强度。结果表明,当 A 的宽度为一(width one)时,其紧致性可在 Zermelo-Fraenkel 公理系统 ZF 中证明;而对其他结构,A 的紧致性会蕴含 3 维空间中不可测集的存在。该结果将约束满足问题的紧致性与选择公理、不可测集等集合论现象联系起来,揭示了宽度条件对逻辑强度的决定性作用。
A finite relational structure A is called compact if for any infinite relational structure B of the same type, the existence of a homomorphism from B to A is equivalent to the existence of homomorphisms from all finite substructures of B to A. We show that if A has width one, then the compactness of A can be proved in the axiom system of Zermelo and Fraenkel, but otherwise, the compactness of A implies the existence of non-measurable sets in 3-space.
DOI 原文 · arXiv · PDF(开放获取) · DBLP
@article{abs-2508-14838,
title = {Constraint satisfaction problems, compactness and non-measurable sets},
author = {Claude Tardif},
journal = {Logical Methods in Computer Science},
volume = {Volume 22, Issue 3},
year = {2026},
doi = {10.46298/lmcs-22(3:1)2026}
}