GumenchukA.I., KrasikovaI.V., and PopovM.M. “Points of Narrowness and Uniformly Narrow Operators”. Carpathian Mathematical Publications 9, no. 1 (June 15, 2017): 37-47. Accessed December 11, 2023. https://scijournals.pnu.edu.ua/index.php/cmp/article/view/1445.