Georgieva, M., and V. Bakeva. “BUSY PERIOD AND NUMBER OF CUSTOMERS SERVED DURING THE BUSY PERIOD IN A GeoX GD 1 QUEUEING SYSTEM”. Matematichki Bilten, vol. 24, no. 1, Jan. 2000, https://bilten.smm.org.mk/index.php/bilten/article/view/1651.