Columbia subject headings:
Communists--Correspondence.
Engels, Friedrich, 1820-1895.
Marx, Karl, 1818-1883.
Harvard subject headings:
Communists--Correspondence
Engels, Friedrich, 1820-1895
Marx, Karl, 1818-1883
Princeton subject headings:
Communists--Correspondence.
Engels, Friedrich, 1820-1895.
Marx, Karl, 1818-1883.