The equation

represents an -D Hypersphere as a quadratic hypersurface in an -D real projective space , where are homogeneous coordinates in . Then the Group of projective transformations which leave invariant is called the Möbius group.

**References**

Iyanaga, S. and Kawada, Y. (Eds.). ``Möbius Geometry.'' §78A in
*Encyclopedic Dictionary of Mathematics.* Cambridge, MA: MIT Press, pp. 265-266, 1980.

© 1996-9

1999-05-26