  The nonadditive entropy introduced by Tsallis in 1988 has been used in
different fields and generalizes the Boltzmann entropy extending the
possibilities of application of the statistical methods developed in the
context of Mechanics. Here we investigate one of the last points of the theory
that still are under discussion: the source term of the nonextensive transport
equation. Based on a simple system, we show that the nonadditivity is a direct
consequence of the phase space topology, and derive the source term that leads
to the nonextensive transport equation.
