Columbia subject headings:
Authors, German--19th century--Correspondence.
Hartleben, Otto Erich, 1864-1905--Correspondence.
Rickert, Heinrich, 1863-1936--Correspondence.
Harvard subject headings:
Hartleben, Otto Erich, 1864-1905--Correspondence.
Rickert, Heinrich, 1863-1936--Correspondence.
Princeton subject headings:
Authors, German--19th century--Correspondence.
Hartleben, Otto Erich, 1864-1905--Correspondence.
Rickert, Heinrich, 1863-1936.