The Holonomy Group I. The Curvature Tensor Vaiclav Hlavaty Indiana University Mathematics Journal 1959 text pdf 10.1512/iumj.1959.8.58020 10.1512/iumj.1959.8.58020 en Indiana Univ. Math. J. 8 (1959) 285 - 307 state-of-the-art mathematics http://iumj.org/access/