NICOLAS PERCSY FINITE MINKOWSKI PLANES IN WHICH EVERY CIRCLE-SYMMETRY IS AN AUTOMORPHISM If a Minkowski plane is finite--i.e, the set of points is finite--all its lines and all its circles have the same number of points q + 1, where q ~> 2 is called the order of the plane. Actually, infinite planes, the 'tangency axiom' (T) is a consequence of the preceding conditions (Heise and Karzel I-6], Percsy [133). Two Minkowski planes M and M' are called isomorphic if there exists an isomorphism from M onto M', i.e. a one-to-one mapping preserving lines and circles. An isomorphism from M on M is called an automorphism of M.
Examples of Minkowski PlanesA classical example of Minkowski plane (the ' Miquelian' plane) is given by the geometry of a ruled quadric Q in a three-dimensional projective space: M is the set of points of Q, ~x and ~2 are the two families of lines contained in Q, and the circles are the non-degenerate plane sections of Q.