Alfred Hettner, who obtained his PhD from the University of Strasbourg, was also a pupil of Ferdinand von Richthofen and Friedrich Ratzel in Leipzig—where he obtained his habilitation. His book Europe was published in 1907. According to him, geography is a chorological science or it is a study of regions. Hettner rejected the view that geography could be either general or regional. Geography like other fields of learning, must deal in both the unique things (regional geography) and with universal (general geography), but the study of regions — especially in the form of his Länderkunde approach — is the main field of geography. Hettner supervised, among others, the PhDs of Oskar Schmieder, Friedrich Metz and Heinrich Schmitthenner.