Gumenchuk, A.I., I.V. Krasikova, and M.M. Popov. “Points of Narrowness and Uniformly Narrow Operators”. Carpathian Mathematical Publications 9, no. 1 (June 15, 2017): 37–47. Accessed April 23, 2024. https://scijournals.pnu.edu.ua/index.php/cmp/article/view/1445.