Chamkha, Y., and M. Kammoun. “On Perturbation of Drazin Invertible Linear Relations”. Ukrains’kyi Matematychnyi Zhurnal 75, no. 2 (March 2, 2023): 269 - 286. Accessed March 28, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/6761.