The author recalls the vector bundle valued differential forms and exterior systems. Then he introduces a new kind of equivalence in order to reformulate the usual concepts of symmetries and infinitesimal symmetries of systems of differential equations: two exterior differential systems are called equivalent if the sets of their solutions coincide, the symmetry is a transformation which changes a given system into an equivalent system.

It is not easy to effectively apply this new conception, a simple example from the relativistic mechanics is nevertheless briefly mentioned.