Kelevedjiev, Emil, Todor Branzov, Petar Petrov, and Marin Shalamanov. “Bulgarian Platform for Competitions in Informatics”. Mathematics and Education in Mathematics 49 (April 7, 2020): 123–130. Accessed November 10, 2026. https://smb.math.bas.bg/mem/index.php/memjournal/article/view/106.