A common characterization of classical and relativistic addition (Q1865868)

The relativistic addition of velocities is considered from the geometer's point of view: he presents an axiomatic form which shows more of the similarities to the classical addition than is usually presented in other places. The underlying idea is to find a parametrization of the velocity space in which the Haar measure of the Lorentz rotations gets a constant density. In the formulas, this becomes obvious from the appearance of the cosh-function.