Gluons from logarithmic slopes of $F_{2}$ in the NLL approximation
  We make a critical, next-to-leading order, study of the accuracy of the Prytz relation, which is frequently used to extract the gluon distribution at small $x$ from the logarithmic slopes of the structure function $F_{2}$. We find that the simple relation is not generally valid in the Hera regime, but show that it is a reasonable approximation for gluons which are sufficiently singular at small $x$. 
K Golec-Biernat