Renormalization of Heavy Quark Effective Field Theory: Quantum Action   Principles and Equations of Motion
  We discuss the quantum action principles and equations of motion for Heavy Quark Effective Field Theory. We prove the so-called equivalence theorem for HQEFT which states that the physical predictions of HQEFT are independent from the choice of interpolating fields. En passant we point out that HQEFT is in fact more subtle than the quantum mechanical Foldy-Wouthuysen transformation. 
Wolfgang Kilian and Thorsten Ohl