Shu, S., and T. Zhu. “Hypersurfaces With Nonzero Constant Gauss – Kronecker Curvature in $M^{n+1}(±1)$”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 68, no. 11, Nov. 2016, pp. 1540-51, http://umj.imath.kiev.ua/index.php/umj/article/view/1940.