Some problems of classification of points in the Desarguesian Hjelmslev plane Rastislav Jurga (1997) Mathematica Slovaca
Squeezing the Accordion in a Strongly n-Uniform Hjelmslev Plane. David A. Drake (1984) Mathematische Zeitschrift
Subspace operations in affine Klingenberg spaces. Bisztriczky, T., Lorimer, J.W. (1995) Bulletin of the Belgian Mathematical Society - Simon Stevin