Merkulov, S. A. Max Planck Institute for Mathematics, Max Planck Society;
Schwachhöfer, L. Max Planck Institute for Mathematics, Max Planck Society;
Merkulov, S. A., & Schwachhöfer, L. (1999). Classification of holonomy groups of free affine connections. Annals of Mathematics, 150(1), 77-149.