Columbia subject headings:
Bulgaria--Foreign relations--Soviet Union--Sources.
Soviet Union--Foreign relations--1975-1985--Sources.
Soviet Union--Foreign relations--Bulgaria--Sources.
Harvard subject headings:
Bulgaria--Foreign relations--Soviet Union--Sources.
Soviet Union--Foreign relations--Bulgaria--Sources.
Princeton subject headings:
Bulgaria--Foreign relations--1944-1990--Sources.
Bulgaria--Foreign relations--Soviet Union--Sources.
Soviet Union--Foreign relations--1975---Sources.
Soviet Union--Foreign relations--Bulgaria--Sources.