Columbia subject headings:
Bŭlgarska komunisticheska partii︠a︡--History.
Communism--Bulgaria--History.
Kommunisticheskai͡a partii͡a Sovetskogo Soi͡uza--History.
Harvard subject headings:
Bulgaria--Relations--Soviet Union.
Bŭlgarska komunisticheska partii︠a︡--History.
Kommunisticheskai͡a partii͡a Sovetskogo Soi͡uza--History.
Soviet Union--Relations--Bulgaria.
Princeton subject headings:
Bulgaria--Relations--Soviet Union.
Bŭlgarska kommunisticheska partii︠a︡--History.
Kommunisticheskai︠a︡ partii︠a︡ Sovetskogo Soi︠u︡za--History.
Soviet Union--Relations--Bulgaria.