一句话:证明弦无爪图类具有LREC_=可定义的正则化,由此得到对数空间同构测试并捕获对数空间与多项式时间。
本文研究描述复杂性中逻辑能否在特定图类上捕获复杂度类。作者证明弦无爪图类允许 LREC_= 可定义的正则化;LREC_= 是在一阶逻辑上加入计数与受限递归算子、可在对数空间求值的逻辑。由此得到弦无爪图的 logspace 正则化算法与同构测试,并且 LREC_= 在该图类上捕获对数空间。又因 LREC_= 包含于带计数的固定点逻辑 FPC,所以 FPC 在该图类上捕获多项式时间。结果连接图类正则化、逻辑表达能力与复杂度类。
We show that the class of chordal claw-free graphs admits LREC$_=$-definable canonization. LREC$_=$ is a logic that extends first-order logic with counting by an operator that allows it to formalize a limited form of recursion. This operator can be evaluated in logarithmic space. It follows that there exists a logarithmic-space canonization algorithm, and therefore a logarithmic-space isomorphism test, for the class of chordal claw-free graphs. As a further consequence, LREC$_=$ captures logarithmic space on this graph class. Since LREC$_=$ is contained in fixed-point logic with counting, we also obtain that fixed-point logic with counting captures polynomial time on the class of chordal claw-free graphs.Comment: 34 pages, 13 figures