However, the largest influence on the direction of his research came from Klein before he was awarded his habilitation, when he studied at the University of Berlin and at the University of Göttingen.
Gayunman, ang pinakamalaking impluwensiya sa direksyon ng kanyang mga pananaliksik na nagmula sa Klein bago siya ay iginawad sa kanyang habilitation, kapag nag-aral siya sa Unibersidad ng Berlin at sa University of Gottingen.