Ali, Nigar, Muhammad Ikhlaq Chohan, and Gul Zaman. “Optimal Control of a Time Delayed HIV-1 Infection Model”. European Journal of Pure and Applied Mathematics 12, no. 2 (April 29, 2019): 506–518. Accessed August 8, 2022. https://ejpam.com/index.php/ejpam/article/view/3416.