Columbia subject headings:
Press, Communist--Bulgaria--History--20th century.
Underground literature--Bulgaria--History--20th century.
Harvard subject headings:
Bulgarian periodicals.
Communism--Bulgaria
Press, Communist--Bulgaria--History--20th century.
Underground literature--Bulgaria--Bibliography.
Underground literature--Bulgaria--History--20th century.
Underground literature--Bulgaria.
Princeton subject headings:
Bulgaria--Politics and government--1878-1944.
Bulgarian periodicals.
Underground press publications--Bulgaria--History--20th century.