On finding periodic solutions of second order difference equations in a Banach spase. Neliniini Kolyvannya, [S. l.], v. 4, n. 3, p. 405–421, 2001. Disponível em: https://twinhead.imath.kiev.ua/index.php/nosc/article/view/184. Acesso em: 22 jan. 2026.