Sato, Yuichiro. “$d$-Minimal Surfaces in Three-Dimensional Singular Semi-Euclidean Space $\mathbb{R}^{0,2,1}$”. Tamkang Journal of Mathematics 52, no. 1 (January 31, 2021): 37-67. Accessed April 10, 2021. https://journals.math.tku.edu.tw/index.php/TKJM/article/view/3045.