Slyusarchuk, V. E. “Refinement of Kneser Theorem on Zeros of Solutions of the Equation $y" + p(x)y = 0$”. Ukrains’kyi Matematychnyi Zhurnal 48, no. 4 (April 25, 1996): 520-524. Accessed May 17, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/5314.