  We describe a phase space generator which is flat for massless particles, and
approximately flat for massive particles of masses much smaller than the
typical mometum scales involved in the process. The same goal is achieved by
the RAMBO algorithm, contrary to which our approach does only require the
minimal number of degrees of freedom and is invertible in the sense that it
provides a unique mapping of random numbers to the physical phase space point
and vice versa. The very motivation to seek such an algorithm is explained in
detail.
