  Dynamical chiral symmetry breaking is a nonperturbative phenomenon that may
be studied using QCD's gap equation. Model-independent results can be obtained
with a nonperturbative and symmetry preserving truncation. The gap equation
yields the massive dressed-quark propagator, which has a spectral
representation when considered as a function of the current-quark mass. This
enables an explication of the connection between the infrared limit of the QCD
Dirac operator's spectrum and the quark condensate appearing in the operator
product expansion.
