Şahin, T., and M. Yilmaz. “On Singularities of the Galilean Spherical Darboux Ruled Surface of a Space Curve in $G_3$”. Ukrains’kyi Matematychnyi Zhurnal 62, no. 10 (October 25, 2010): 1377–1387. Accessed April 24, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/2962.