Ganchev, G., and V. Mihova. “A CLASSIFICATION OF CONFORMALLY FLAT RIEMANNIAN MANIFOLDS LOCALLY ISOMETRIC TO HYPERSURFACES IN EUCLIDEAN OR MINKOWSKI SPACE”. Ann. Sofia Univ. Fac. Math. And Inf., vol. 102, Dec. 2015, pp. 109-32, https://ftl5.uni-sofia.bg./index.php/fmi/article/view/66.