The process of continuing away from dimension 4 is not completely well defined without a prescription for how to do it. The prescription is only well defined on diagrams. It replaces the Schwinger representation in dimension 4 with the Schwinger representation in dimension 4 − ε defined by: G ( x − − y ) = ∫ ∫ d τ τ 1 t d 2 e x 2 2 τ τ + t τ τ