Ning B, Zhai M. Counting Substructures and Eigenvalues II: Quadrilaterals. Electron. J. Combin. [Internet]. 2025Oct.3 [cited 2026May30];32(4):#P4.1. Available from: https://www.combinatorics.org/ojs/index.php/eljc/article/view/v32i4p1