Dirac's hole theory versus quantum field theory
  Dirac's hole theory and quantum field theory are usually considered equivalent to each other. For models of a certain type, however, the equivalence may not hold as we discuss in this Letter. This problem is closely related to the validity of the Pauli principle in intermediate states of perturbation theory. 
F.A.B. Coutinho, D. Kiang, Y. Nogami and Lauro Tomio