Closure conditions in the nets
Reflection loops of spaces with congruence and hyperbolic incidence structure
In an absolute space with congruence there are line reflections and point reflections. With the help of point reflections one can define in a natural way an addition + of points which is only associative if the product of three point reflection is a point reflection again. In general, for example for the case that is a linear space with hyperbolic incidence structure, the addition is not associative. is a K-loop or a Bruck loop.
Some combinatorial properties of conics in the Hjelmslev plane
Special automorphisms of nets with Baer subnets
Ternary spaces, media, and Chebyshev sets