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