RAFFOUL, Youssef N.; YANKSON, Ernest. Positive periodic solutions of functional discrete systems with a parameter. CUBO, A Mathematical Journal, [S. l.], v. 21, n. 1, p. 79–90, 2019. DOI: 10.4067/S0719-06462019000100079. Disponível em: https://cubo.ufro.cl/index.php/cubo/article/view/2120. Acesso em: 24 may. 2025.