On a question of Haemers regarding vectors in the nullspace of Seidel matrices

Saieed Akbari, Sebastian M. Cioabă, Samira Goudarzi +2

In 2011, Haemers asked the following question: If $S$ is the Seidel matrix of a graph of order $n$ and $S$ is singular, does there exist an eigenvector of $S$ corresponding to $0$…