Shu, Shichang, and Tianmin Zhu. “Hypersurfaces With Nonzero Constant Gauss – Kronecker Curvature in $M^{n+1}(±1)$”. Ukrains’kyi Matematychnyi Zhurnal 68, no. 11 (November 25, 2016): 1540-1551. Accessed October 5, 2022. http://umj.imath.kiev.ua/index.php/umj/article/view/1940.