Sophus Lie, Friedrich Engel and the Riemann-Helmholtz problem
arXiv:0910.0801
Abstract
A focused modernization of Sophus Lie's brilliant writings about the foundations of geometry that every contemporary geometer should have at least once a look at. Translated, updated, commented.
Monograph accepted (without revision) by Hermann Editeurs, rue de la Sorbonne, Paris, 5 February 2010. New thanks addressed to a leading international expert; a few references added