ABSTRACT
This chapter discusses what general properties a commutator has to have in momentum space, such that its Fourier transform will be zero outside the light cone of configuration space. This is clearly a promising line to follow to supplement physical intuition on the properties of Wµ?. A far more subtle and useful observation was made by Dyson. He noticed, in many problems we also know C(q) = 0 for certain regions of q space. One of the difficulties in using the Dyson representation is that the function F is not unique, many can give the same C(q). c This is, of course, just Dyson's representation if the four vector uµ can be assumed to have only a time component, that is, only a component in the pµ direction.
