Logical complexity of graphs: a survey

We discuss the definability of finite graphs in first-order logic with two relation symbols for adjacency and equality of vertices. The logical depth D(G) of a graph G is equal to the minimum quantifier depth of a sentence defining G up to isomorphism. The logical width W(G) is the minimum number of variables occurring in such a sentence. The logical length L(G) is the length of a shortest defining sentence. We survey known estimates for these graph parameters and discuss their relations to other topics (such as the efficiency of the WeisfeilerLehman algorithm in isomorphism testing, the evolution of a random graph, or the contribution of Frank Ramsey to the research on Hilbert's Entscheidungsproblem). Also, we trace the behavior of the descriptive complexity of a graph as the logic becomes more restrictive (for example, only definitions with a bounded number of variables or quantifier alternations are allowed) or more expressible (after powering with counting quantifiers). Date: ...

• Type: Journal
• Year: 2010
• Where: CORR
• Authors: Oleg Pikhurko, Oleg Verbitsky
• Keywords: Alexander Von Humboldt Foundation, CORR 2010, Education, Minimum Quantifier Depth, Shortest Defining Sentence