PACHPATTE, B. G. OPIAL TYPE DISCRETE INEQUALITIES IN TWO VARIABLES. Tamkang Journal of Mathematics, [S. l.], v. 22, n. 4, p. 323–328, 1991. DOI: 10.5556/j.tkjm.22.1991.4616. Disponível em: https://journals.math.tku.edu.tw/index.php/TKJM/article/view/4616. Acesso em: 25 apr. 2024.