Columbia subject headings:
Shumen (Bulgaria : Oblast)--History--Sources.
World War, 1939-1945--Underground movements--Bulgaria--Shumen (Oblast)--Sources.
Harvard subject headings:
Shumenski okrŭg (Bulgaria)--History--Sources.
World War, 1939-1945--Underground movements--Bulgaria--Shumenski okrŭg--Sources.
Princeton subject headings: