The Weisfeiler-Leman algorithm and recognition of graph properties

Abstract

The k-dimensional Weisfeiler-Leman algorithm (k-WL) is a very useful combinatorial tool in graph isomorphism testing. We address the applicability of k-WL to recognition of graph properties. Let G be an input graph with n vertices. We show that, if n is prime, then vertex-transitivity of G can be seen in a straightforward way from the output of 2-WL on G and on the vertex-individualized copies of G. This is perhaps the first non-trivial example of using the Weisfeiler-Leman algorithm for recognition of a natural graph property rather than for isomorphism testing. On the other hand, we show that, if n is divisible by 16, then k-WL is unable to distinguish between vertex-transitive and non-vertex-transitive graphs with n vertices unless k=Ω(n). Similar results are obtained for recognition of arc-transitivity. Our lower bounds are based on an analysis of the Cai-Fürer-Immerman construction, which might be of independent interest. In particular, we provide sufficient conditions under which the Cai-Fürer-Immerman graphs can be made colorless.