GUNDERSEN, G. G. Solutions of f " + P(z)f = 0 that have almost all real zeros. Annales Fennici Mathematici, [S. l.], v. 26, n. 2, p. 483–488, 2001. Disponível em: https://afm.journal.fi/article/view/135018. Acesso em: 4 apr. 2025.