  The formal consideration of the concept of interaction in thermodynamic
analysis makes it possible to deduce, in the broadest terms, new results
related to the coevolution of interacting systems, irrespective of their
distance from thermodynamic equilibrium. In this paper I prove the existence of
privileged coevolution trajectories characterized by the minimum joint
production of internal entropy, a conclusion that extends Prigogine theorem to
systems evolving far from thermodynamic equilibrium. Along these trajectories
of minimum internal entropy production one of the system goes always ahead of
the other with respect to equilibrium.
