@unpublished{ManicciaMughetti2008,
  author  = {L. Maniccia and M. Mughetti},
  title   = {Weyl calculus for a class of subelliptic operators},
  institution = {Institut f{\"u}r Mathematik},
  series    = {Preprint},
  number    = {(2001) 19},
  year    = {2008},
}