Tran Van An, and Nguyen Van Dung. “$ls$-Ponomarev-Systems and Compact Images of Locally Separable Metric Spaces”. Methods of Functional Analysis and Topology 15, no. 4 (December 25, 2009): 391–400. Accessed December 16, 2025. https://zen.imath.kiev.ua/index.php/mfat/article/view/433.