Iterated Riesz Commutators: A Simple Proof of Boundedness
  We give a simple proof of L^p boundedness of iterated commutators of Riesz transforms and a product BMO function. We use a representation of the Riesz transforms by means of simple dyadic operators - dyadic shifts - which in turn reduces the estimate quickly to paraproduct estimates. 
Michael T. Lacey, Stefanie Petermichl, Jill C. Pipher, Brett D. Wick