"The discovery of asymptotic freedom might make it seem obvious that Feynman diagrams would now litter physicists' scratch pads and blackboards even more densely than before. After all, Dyson had domesticated Feynman's diagrams in the first place as aids for making perturbative calculations. Yet asymptotic freedom did not herald a straight forward return to Dyson's original techniques. For one thing, writing down the so-called Feynman rules proved formidable in the new models."