Columbia subject headings:
Fellner, Ferdinand, 1847-1916.
Helmer, Hermann Gottlieb, 1849-1919.
Harvard subject headings:
Fellner, Ferdinand, 1847-1916.
Helmer, Hermann Gottlieb, 1849-1919.
Princeton subject headings:
Fellner, Ferdinand, 1847-1916.
Helmer, Hermann, 1849-1919.