BRONO, A. M., and Abba Gana kachalla Ali. “I_2-Statistical Limit Superior and I_2–Statistical Limit Inferior for Double Sequences”. Journal of the Nigerian Mathematical Society 39, no. 3 (January 8, 2021): 323–333. Accessed April 12, 2021. https://ojs.ictp.it/jnms/index.php/jnms/article/view/323.