Columbia subject headings:
Harvard subject headings:
Dertliev, Petŭr, 1916---Correspondence.
Politicians--Bulgaria--Correspondence.
Prisoners--Bulgaria--Correspondence.
Princeton subject headings:
Bulgaria--History--1944-1990.
Dertliev, Petŭr, 1916---Correspondence.
Political persecution--Bulgaria--History--20th century.
Political prisoners--Bulgaria--Correspondence.
Politicians--Bulgaria--Correspondence.