  We show that the Politzer theorem on the equations of motion implies
approximate constraints on the quark correlator, restricting considerably, for
sufficiently large Q^2, the number of independent distribution functions that
characterize the internal structure of the nucleon, and of independent
fragmentation functions. This result leads us to suggesting an alternative
method for determining transversity. Moreover our approach implies predictions
on the Q^2-dependence of some azimuthal asymmetries, like Sivers, Qiu-Sterman
and Collins asymmetry. Lastly, we discuss some implications on the
Burkhardt-Cottingham and Efremov-Leader-Teryaev sum rules.
