Georgieva, Magdalena, and Verica Bakeva. “BUSY PERIOD AND NUMBER OF CUSTOMERS SERVED DURING THE BUSY PERIOD IN A \(Geo^X G_D 1\) QUEUEING SYSTEM”. Matematichki Bilten, vol. 24, no. 1, Jan. 2000, pp. 121-30, https://bilten.smm.org.mk/index.php/bilten/article/view/1651.