1. Kobayashi & Nomizu, Foundations of Differential Geometry, Vol. I, Interscience, New York (1963)
2. Y.M. Cho, Einstein Lagrangian as the translational Yang-Mills Lagrangian,Phys Rev D 14 No 10 (1976)
3. F.W. Hehl, J. Nitsch, P. von der Heyde, Gravitation and Poincaré Gauge Field Theory with Quadratic Lagrangian, preprint, University of Cologne, West Germany (1978)
4. A. Trautman, On the structure of the Einstein-Cartan equations, Symposia Mathematica 12, 139 NY (1973)