@unpublished{SchulzeSterninSavin2008,
  author  = {Bert-Wolfgang Schulze and Boris Sternin and Anton Savin},
  title   = {The homotopy classification and the index of boundary value problems for general elliptic operators},
  institution = {Institut f{\"u}r Mathematik},
  series    = {Preprint},
  number    = {(1999) 20},
  year    = {2008},
}