The Overlap-Dirac Operator: Topology and Chiral Symmetry Breaking
  We review the spectral flow techniques for computing the index of the overlap Dirac operator including results relevant for SUSY Yang-Mills theories. We describe properties of the overlap Dirac operator, and methods to implement it numerically. We use the results from the spectral flow to illuminate the difficulties in numerical calculations involving domain wall and overlap fermions. 
R.G. Edwards, U.M. Heller, R. Narayanan