1. Generalities, and known results 1.1 Definitions. A stable plane is a linear space M = (M , M), where the point space M and the line space M are endowed with locally compact topologies such that joining of points and intersection of lines are continuous operations, and that the set of pairs of intersecting lines is open in M × M (axiom of stability). Moreover, we require that the point space M has positive and finite (topological) dimension. Whenever this is convenient, we shall tacitly identify a line of a stable plane with the set of points that are incident with it. The line that joins p, q ∈ M is written pq, and the pencil of all lines that are incident with a point p will be denoted by M p . General information about stable planes can be found in the work of R. Löwen; in particular, see [3] and [7]. Most important is the deep result [7, Theorem 1] that dim M = dim M = 2 dim M p = 2 dim(pq) ∈ {2, 4, 8, 16}. For recent developments of the theory, compare also [23]. Endowed with the compact-open topology derived from the action on M (or on M), the group Aut(M) of all continuous collineations of M is a locally compact transformation group both on M and M.