Boua, H. “Upper Semi-Fredholm and Kato Spectrum of an $\alpha$-Times Integrated Semigroup”. Methods of Functional Analysis and Topology 26, no. 1 (March 25, 2020): 63–67. Accessed February 4, 2026. https://zen.imath.kiev.ua/index.php/mfat/article/view/744.