Strongly regular graphs with second eigenvalue 6 and =0

J. Koolen proposed the problem of studying distance-regular graphs in which the neighborhoods of vertices are strongly regular graphs with second eigenvalue ≤ t for a given positive integer t. Earlier Koolen’s problem was solved for t ≤ 5. In this paper we consider strongly regular graphs with second eigenvalue 6 and λ=0. They are neighborhoods of vertices of distance-regular graphs satisfying the Koolen’s problem for t=6.