  Using the previously derived confining gluon propagator, the corresponding
system of equations determining the quark propagator is derived. The system of
equations consists of the Schwinger-Dyson equation for the quark propagator
itself, which includes the zero momentum transfer quark-gluon vertex. It is
complemented by the Slavnov-Taylor identity for this vertex. The quark equation
depends explicitly on the mass gap, determining the scale of the truly
nonperturbative dynamics in the QCD ground state. The obtained system of
equations is manifestly gauge-invariant, i.e., does not depend explicitly on
the gauge-fixing parameter. It is also free from all the types of the
perturbative contributions ("contaminations"), which may appear at the
fundamental quark-gluon level.
