@TechReport{BrandtKuesters+-LTCS-01-06,
  author =       {S.~Brandt and R.~K{\"u}sters and A.-Y.~Turhan},
  title =        {Approximation and Difference in Description Logics},
  institution =  {LuFG Theoretical Computer Science, RWTH Aachen},
  year =         2001,
  type =         {LTCS-Report},
  number =       {01-06},
  address =      {Germany}
}