In this paper, we study the expressive power of revised Datalog on the problems that are closed under substructures. We show that revised Datalog cannot define all the problems that are in PTIME and closed under substructures. As a corollary, LFP cannot define all the extension-closed problems that are in PTIME.

翻译：本文研究修正Datalog在子结构封闭问题上的表达能力。我们证明修正Datalog无法定义所有属于PTIME且对子结构封闭的问题。作为推论，LFP无法定义所有属于PTIME且对扩张封闭的问题。