Klaczak, Jerzy. “Kneser Oscillation Theorem for Differential Equations With Piecewise Constant Argument”. Annales Mathematicae Silesianae 5 (September 30, 1991): 51-56. Accessed November 24, 2024. https://journals.us.edu.pl/index.php/AMSIL/article/view/14281.