A. Hammodat, Alaa, Ali A. Bilal, and Akram S. Mohammed. “Some Basic Properties of Idempotent Matrices”. Journal of Education and Science 21, no. 4 (December 1, 2008): 124–130. Accessed September 10, 2025. https://edusj.uomosul.edu.iq/index.php/edusj/article/view/42404.