Klein, however, was fascinated by Riemann's geometric approach and he wrote a book in 1892 giving his version of Riemann's work yet written very much in the spirit of Riemann. Freudenthal writes in:
Klein, gayunman, ay nabighani sa pamamagitan ng Riemann's geometriko diskarte at siya wrote isang libro sa 1892 na nagbibigay sa kanyang bersyon ng Riemann ng trabaho pa nakasulat na tunay marami sa diwa ng Riemann. Freudenthal magsusulat sa: