  In 1976 't Hooft introduced an elegant approach towards understanding the
physical consequences of the topological structures that appear in non-Abelian
gauge theories. These effects are concisely summarized in terms of an effective
multi-fermion interaction. These old arguments provide a link between a variety
of recent and sometimes controversial ideas including discrete chiral
symmetries appearing in some models for unification, ambiguities in the
definition of quark masses, and flaws with some simulation algorithms in
lattice gauge theory.
