APA

Vulkov G., Venkov V. K., . (1986). Code name Unterwelt. : Sofia Press.

Chicago

Vulkov Georgi, Venkov Ventsislav K, . 1986. Code name Unterwelt. : Sofia Press.

Harvard

Vulkov G., Venkov V. K., . (1986). Code name Unterwelt. : Sofia Press.

MLA

Vulkov Georgi, Venkov Ventsislav K, . Code name Unterwelt. : Sofia Press. 1986.