Chubykalo, A., A. Espinoza, and V. Kuligin. “Spatial Curvature As a Distorted Mapping of Euclidean Space”. Boson Journal of Modern Physics, Vol. 4, no. 2, Oct. 2018, pp. 435-42, http://scitecresearch.com/journals/index.php/bjmp/article/view/1632.