On a functional equation arising from hyperbolic geometry.
On Blocking Sets in Affine Hjelmslev Planes
ACM Computing Classification System (1998): G.2.1.We prove that the minimum size of an affine blocking set in the affine plane AHG ...This research has been supported by the Scientific Research Fund of Sofia University under Contract No 109/09.05.2012.
On mappings preserving a single Lorentz-Minkowski-distance in Hjelmslev's classical plane.