Todorov, V., Apostolova, M., Brankova, E., Zlateva, S., Teneva, V., & Khristov, D. (1997). Study of the scientific work by quantitative methods: some results on Academician Nikola Obreshkoff’s works. Ann. Sofia Univ. Fac. Math. And Inf., 89, 117–127. Retrieved from https://stipendii.uni-sofia.bg/index.php/fmi/article/view/361