Issues in Leading Particle and Charm Production in DIS at HERA
  A Monte Carlo simulation based on O(alpha_s) QCD matrix elements matched to parton showers shows that final-state hadrons in deep inelastic scattering (DIS) can be used to tag events with a single (anti)quark recoiled against the proton. The method is particularly suited to study the mean charge of leading particles, which is sensitive to fragmentation and sea quark contribution to the proton structure function. We also discuss methods to study the charm production in DIS using the Breit frame. 
S. V. Chekanov (ANL)