1. H. Karzel. Recent developments on absolute geometries and algebraization by K-loops. Discrete Math. 208/209 (1999), 387–409.
2. H. Karzel, H.-J. Kroll. Geschichte der Geometrie seit Hilbert, Wissenschaftliche Buchgesellschaft, Darmstadt, 1988.
3. H.Karzel, M.Marchi. Introduction of Measures for Segments and Angles in a general Absolute Plane, Discrete Math. (submitted).
4. H.Karzel, M.Marchi. Classification of general absolute geometries with Lambert-Saccheri quadrangles, (to appear).
5. H.Karzel, M.Marchi. The defect in an invariant Reflection Structure (to appear).