Tadee, S., and U. Pintoptang. βOn the Non-Linear Diophantine Equations $4^{x} - a^{y} = dz^{2}$ and $4^{x} + a^{y} = dz^{2}$β. Thai Journal of Mathematics, vol. 21, no. 3, Sept. 2023, pp. 563β567, https://thaijmath2.in.cmu.ac.th/index.php/thaijmath/article/view/1527.