@unpublished{HarutjunjanSchulze2009,
  author  = {G. Harutjunjan and Bert-Wolfgang Schulze},
  title   = {Conormal symbols of mixed elliptic problems with singular interfaces},
  institution = {Institut f{\"u}r Mathematik},
  series    = {Preprint},
  number    = {(2005) 12},
  year    = {2009},
}