Dursun, U., and N. C. Turgay. “Space-Like Surfaces in Minkowski Space $E^4_1$ With Pointwise 1-Type Gauss Map”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 71, no. 1, Jan. 2019, pp. 59-72, https://umj.imath.kiev.ua/index.php/umj/article/view/1419.