  The bare-dressed technique is, for the first time, used in collision theory.
The approach is valid for classical as well for quantum binary elastic
collisions in the non relativistic regime. The same formalism can be used for
inelastic collisions, when the particles undergo only a change of their
internal quantum states during the collision process. All kinematic results can
be obtained by a simple matrix transformation. Moreover, to make also simple
and clear the results, for the inelastic collisions, the restitution
coefficient formulation of inelastic processes has been used.
