PotapenkoI. V. “Relationship Between Normalized Tensors of Two Regular Networks on the Surfaces in the Euclidean Space $E_3$”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 68, no. 2, Feb. 2016, pp. 271-7, http://umj.imath.kiev.ua/index.php/umj/article/view/1839.