Tang, Quanyu, and Clive Elphick. “Proof of a Conjectured Spectral Upper Bound on the Chromatic Number of a Graph”. The Electronic Journal of Combinatorics 33, no. 2 (June 19, 2026): #P2.65. Accessed June 18, 2026. https://www.combinatorics.org/ojs/index.php/eljc/article/view/v33i2p65.