Kiosak, V. A., and G. V. Kovalova. “ Geodesic Mappings of Quasi-Einstein Spaces With a Constant Scalar Curvature”. Matematychni Studii 53, no. 2 (June 24, 2020): 212-217. Accessed April 25, 2024. http://matstud.org.ua/ojs/index.php/matstud/article/view/13.