SLYUSARCHUK, V. E. Refinement of Kneser theorem on zeros of solutions of the equation $y" + p(x)y = 0$. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 48, n. 4, p. 520–524, 1996. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/5314. Acesso em: 5 dec. 2025.