When I teach hyperbolic geometry, I use the Hjelmslev
Transformation. Do you know where he published his transformation, and
of what his exposition of it consisted.]]
Perhaps Ken Pledger's recent posting on Hjelmslev helps.
I'm concerned, however, with the respects in which the
nat.geom. and wirk.geom. papers of Hjelmslev influenced his
mathematical/geometric con structions.
best,
robert tragesser