摘要: Abstract The analogue for leptoproduction of the Sterman-Weinberg jet formula is derived. 2-jet fraction calculated in first order QCD and explicitly shown to be free mass singularities. Approximations made derivation limit phenomenological usefulness but, by studying quark isolation, a related greater applicability also obtained. Certain qualitative features properties perturbative (notably x Bj y dependence at fixed W ) are emphasized contrasted with fragmentation picture. Quark jets quantitatively different from e + − annihilation.