@unpublished{BuchholzSchulze2008,
  author  = {Thilo Buchholz and Bert-Wolfgang Schulze},
  title   = {Volterra operators and parabolicity : anisotropic pseudo-differential operators},
  institution = {Institut f{\"u}r Mathematik},
  series    = {Preprint},
  number    = {(1998) 11},
  year    = {2008},
}