  Planar L-loop maximally helicity violating amplitudes in N = 4 supersymmetric
Yang-Mills theory are believed to possess the remarkable property of satisfying
iteration relations in L. We propose a simple new method for studying the
iteration relations for four-particle amplitudes which involves the use of
certain linear differential operators and eliminates the need to fully evaluate
any loop integrals. We carry out this procedure in explicit detail for the
two-loop amplitude and argue that this method can be used to prove the
iteration relations to all loops up to polynomials in logarithms.
