Georgieva, Magdalena, and Verica Bakeva. “SOME CHARACTERISTICS OF OUTPUT STREAM OF UNSERVED CUSTOMERS IN \(G^X G 1\) AND \(G_D^X G_D 1\) SYSTEM”. Matematichki Bilten, vol. 24, no. 1, Jan. 2000, pp. 131-40, https://bilten.smm.org.mk/index.php/bilten/article/view/1652.