论文标题

关系结构的图:受限类型

Graphs of relational structures: restricted types

论文作者

Bulatov, Andrei A.

论文摘要

约束满意度问题的代数方法(CSP)使用关系结构的高阶对称性(多态性)来研究CSP的复杂性。在本文中,我们进一步开发了可以实施代数方法的方法之一,并将其​​应用于某些类型的CSP。该方法是在我们的LIC 2004论文中引入的,涉及对有限代数和关系结构的局部结构的研究。它与代数a或一个关系结构相关联,其顶点是A(或s)的元素,边缘代表A的子集,以至于a在子集上的某个术语操作的限制是“良好的”,即是3种类型的操作:半静脉,大型,大型,大型或仿射。在本文中,我们使用该理论,并考虑具有限制类型的边缘的代数。我们证明类型限制保留在标准代数结构下。然后我们表明,如果关系结构中的类型边缘受到限制,则可以通过特定算法在多项式时间内求解相应的CSP。特别是,我们给出了一个新的,更直观的证据,证明了有界宽度定理:代数A上方的CSP在且仅当A不包含仿射边缘时具有界限宽度。实际上,该结果表明界限宽度意味着宽度(2,3)。最后,我们证明,没有半层次边缘的代数几乎没有幂的亚代数,也就是说,这种代数上的CSP也是多项式时间。本文获得的方法和结果是作者2017年二分法猜想的重要成分。 Zhuk也独立证明了二分法的猜想。

The algebraic approach to the Constraint Satisfaction Problem (CSP) uses high order symmetries of relational structures -- polymorphisms -- to study the complexity of the CSP. In this paper we further develop one of the methods the algebraic approach can be implemented, and apply it to some kinds of the CSP. This method was introduced in our LICS 2004 paper and involves the study of the local structure of finite algebras and relational structures. It associates with an algebra A or a relational structure S a graph, whose vertices are the elements of A (or S), the edges represent subsets of A such that the restriction of some term operation of A is `good' on the subset, that is, act as an operation of one of the 3 types: semilattice, majority, or affine. In this paper we use this theory and consider algebras with edges from a restricted set of types. We prove type restrictions are preserved under the standard algebraic constructions. Then we show that if the types edges in a relational structure are restricted, then the corresponding CSP can be solved in polynomial time by specific algorithms. In particular, we give a new, somewhat more intuitive proof of the Bounded Width Theorem: the CSP over algebra A has bounded width if and only if A does not contain affine edges. Actually, this result shows that bounded width implies width (2,3). Finally, we prove that algebras without semilattice edges have few subalgebras of powers, that is, the CSP over such algebras is also polynomial time. The methods and results obtained in this paper are important ingredients of the 2017 proof of the Dichotomy Conjecture by the author. The Dichotomy Conjecture was also proved independently by Zhuk.

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