A projective model is given by a hyperbolic linear congruence of lines in a projective 3-space over F , i.e., the set of all lines that meet two skew axes. As above, the F -chains appear exactly as the reguli contained in the congruence. Such a congruence has just one axis which belongs to the congruence. The axis is the only line of the congruence that represents no point of the dual projective line. As in the hyperbolic case, all lines of the congruence through a point on the axis form a pencil.
P is a projectivity.
The F -chains appear exactly as the reguli contained in the congruence. The F -chains appear exactly as the reguli that have the axis of the complex among its transversals. Eine affine Beschreibung von Ketten, Abh. On the Geometry of Field Extensions, Aequat. math. Chain Spaces over Jordan Systems, Abh.