Key points are not available for this paper at this time.
Arguments of positivity and conformal invariance in the Gell-Mann-Low limit imply positive anomalies ₍ ₍= (scaledimension) -2-N for the operators O₁{₍} (N0) which occur in the light-cone expansion of two currents.
Ferrara et al. (Sat,) studied this question.