code: public static IndexForVc getConfigIter(VarSet indexVars, VarConfig config) {
          int fixedConfigContrib = getConfigIndex(indexVars, config);
          VarSet forVars = new VarSet(indexVars);
          forVars.removeAll(config.getVars());
          return new IndexForVc(indexVars, forVars, fixedConfigContrib);
      }
docs: Iterates over all the configurations of indexVars where the subset of
  variables in config have been clamped to their given values. The
  iterator returns the configuration index of variables in indexVars.
  
  @param indexVars Variable set over which to iterate.
  @param config Clamped assignment.
  @return Iterator.