Columbia subject headings:
Engels, Friedrich, 1820-1895.
Marx, Karl, 1818-1883.
Socialists--Biography.
Harvard subject headings:
Engels, Friedrich, 1820-1895
Marx, Karl, 1818-1883
Socialists--Biography
Princeton subject headings:
Engels, Friedrich, 1820-1895.
Marx, Karl, 1818-1883.
Socialists--Correspondence, reminiscences, etc.