Abiad, Aida, and Willem H Haemers. “Cospectral Graphs and Regular Orthogonal Matrices of Level 2”. The Electronic Journal of Combinatorics 19, no. 3 (August 9, 2012): P13. Accessed April 4, 2026. https://www.combinatorics.org/ojs/index.php/eljc/article/view/v19i3p13.