Bacher, Roland. “Counting Invertible Schrödinger Operators over Finite Fields for Trees, Cycles and Complete Graphs”. The Electronic Journal of Combinatorics 22, no. 4 (December 11, 2015): P4.40. Accessed March 27, 2026. https://www.combinatorics.org/ojs/index.php/eljc/article/view/v22i4p40.