SLYUSARCHUK, V. Yu. Strengthening of the Kneser theorem on zeros of solutions of the equation $u″ + q(t)u = 0$ using one functional equation. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 62, n. 12, p. 1705–1714, 2010. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/2993. Acesso em: 17 apr. 2025.