一句话:证明 (1-in-3-SAT, Not-All-Equal-3-SAT) 不能自然归约到可解有限域 CSP,除非 P=NP。
承诺约束满足问题(PCSP)是固定模板 CSP 的重要推广,涵盖可满足性与图着色等问题的近似变体。目前已知所有有限模板上多项式可解的 PCSP 都能以某种自然方式归约到可解的 CSP,但这些 CSP 往往定义在无穷域上。本文研究这种无穷性是否必要。作者聚焦一个具体的有限域 PCSP,即 (1-in-3-SAT, Not-All-Equal-3-SAT),通过复杂性理论论证与归约分析,证明除非 P=NP,否则该 PCSP 不能自然归约到任何可解的有限域 CSP。这一结果说明,对有限域 PCSP 而言,归约目标出现无穷域并非技术偶然,而是本质需要;它为 PCSP 的代数/复杂性分类划定了边界。
The fixed template Promise Constraint Satisfaction Problem (PCSP) is a recently proposed significant generalization of the fixed template CSP, which includes approximation variants of satisfiability and graph coloring problems. All the currently known tractable (i.e., solvable in polynomial time) PCSPs over finite templates can be reduced, in a certain natural way, to tractable CSPs. However, such CSPs are often over infinite domains. We show that the infinity is in fact necessary by proving that a specific finite-domain PCSP, namely (1-in-3-SAT, Not-All-Equal-3-SAT), cannot be naturally reduced to a tractable finite-domain CSP, unless P=NP.