  We propose a self-consistent scheme for the determination of the ground-state
(GS) properties of interacting electrons in a magnetic field, and of systems
whose GS's time-reversal-symmetry (TRS) is spontaneously broken. It is based on
a newly-developed many-body perturbation theory that is valid, irrespective of
the strength of correlation, provided the GS number densities
$n_{\uparrow}({\bf r})$, $n_{\downarrow}({\bf r})$, and the {\sl total}
paramagnetic particle flux density are pure-state non-interacting
$v$-representable. Our approach can in particular be applied to (modulated)
two-dimensional electron systems in the fractional quantum-Hall regime.
