Sherif, Nagwa. “On Transformations and Perturbations of Orthogonal R-Frames”. Rev. Téc. Fac. Ing. Univ. Zulia 14, no. 2 (February 16, 2011). Accessed December 5, 2025. http://www.produccioncientificaluz.org/index.php/tecnica/article/view/5384.