V. Subprabha, P. T. Infant Vijula, and N. Durga Devi. 2021. “A New Closure Operator via $(1,2) S_\beta$-Open Sets in Bi-Topological Spaces”. Malaya Journal of Matematik 9 (01). India:1114-17. https://www.malayajournal.org/index.php/mjm/article/view/1232.