Mahi F., and BelkhelfaM. “Legendrian Normally Flat Submanifols of $\mathcal{S}$-Space Forms”. Carpathian Mathematical Publications 12, no. 1 (June 12, 2020): 69-78. Accessed June 22, 2021. https://scijournals.pnu.edu.ua/index.php/cmp/article/view/3878.