Existence theory for single and multiple periodic and almost periodic solutions of nonlinear integral equations. Neliniini Kolyvannya, [S. l.], v. 4, n. 1, p. 2–15, 2001. Disponível em: https://twinhead.imath.kiev.ua/index.php/nosc/article/view/151. Acesso em: 22 jan. 2026.