  Virtual quark effects in lattice QCD are studied in an approach where the
infrared modes are included in a precise and gauge-invariant manner. At fixed
physical volume the required number of modes does not increase in the continuum
limit, and the acceptance is tolerable even for very light quark masses.
Topological charge distributions at varying quark mass, and the static quark
potential, showing the onset of string-breaking, are presented in both QED2 and
QCD4.
