Homotopy type of Neighborhood Complexes of Kneser graphs, $K{G}_{2,k}$

Abstract

Schrijver identified a family of vertex critical subgraphs of the Kneser graphs called the stable Kneser graphs $S{G}_{n,k}$. Björner and de Longueville proved that the neighborhood complex of the stable Kneser graph $S{G}_{n,k}$ is homotopy equivalent to a $k-$sphere. In this article, we prove that the homotopy type of the neighborhood complex of the Kneser graph $K{G}_{2,k}$ is a wedge of $(k+4)(k+1)+1$ spheres of dimension $k$. We construct a maximal subgraph $S_{2,k}$ of $K{G}_{2,k}$, whose neighborhood complex is homotopy equivalent to the neighborhood complex of $S{G}_{2,k}$. Further, we prove that the neighborhood complex of $S_{2,k}$ deformation retracts onto the neighborhood complex of $S{G}_{2,k}$.

arXiv comment11 pages