  It is argued from geometrical, group-theoretical and physical points of view
that in the framework of QCD it is not only necessary but also possible to
modify the Dirac equation so that correspondence principle holds valid. The
Dirac wave equation for a quark is proposed and some consequences are
considered. In particular, it is shown that interquark potential expresses the
Coulomb law for the quarks and, in fact, coincides with the known Cornell
potential.
