Mohammed, Ramadhan, and Ramziya Ameen. “Soft ξ-Open Sets in Soft Topological Spaces”. Science Journal of University of Zakho 7, no. 3 (September 30, 2019): 108-119. Accessed November 20, 2019. https://sjuoz.uoz.edu.krd/index.php/sjuoz/article/view/598.