Columbia subject headings:
Harvard subject headings:
Adler, Victor, 1852-1918--Correspondence--Sources.
Adler, Victor, 1852-1918--Correspondence.
Communists--Germany--Correspondence.
Engels, Friedrich, 1820-1895--Correspondence--Sources.
Engels, Friedrich, 1820-1895--Correspondence.
Socialists--Austria--Correspondence.
Princeton subject headings:
Adler, Victor, 1852-1918--Correspondence.
Engels, Friedrich, 1820-1895--Correspondence.