微分几何

　　This book is a study of an aspect of Elie Cartan's contribution to thequestion "What is geometry?"
　　In the last century two great generalizations of Euclidean geometry ap-peared. The first was the discovery of the non-Euclidean geometries. Thesewere organized into a coherent whole by Felix Klein, who recognized themas various examples of coset spaces G/H of Lie groups. In this book we refer to these latter as Klein geometries. The second generalization was Georg Riemann's discovery of what we now call Riemannian geometry. These two theories seemed largely incompatible with one other.1
　　In the early 1920s Elie Cartan, one of the pioneers of the theory of Lie groups, found that it was possible to obtain a common generalization of these theories, which he called espaces generalizes and we call Cartan geometries (see diagram).