Team, S. “Notes on the Spectrum of Lower Triangular Double-Band Matrices: Ali M. Akhmedov, Saad R. El-Shabrawy”. Thai Journal of Mathematics, vol. 10, no. 2, Aug. 2012, pp. 415-21, https://thaijmath2.in.cmu.ac.th/index.php/thaijmath/article/view/328.