@unpublished{SchulzeSavinSternin2008,
  author  = {Bert-Wolfgang Schulze and Anton Savin and Boris Sternin},
  title   = {Elliptic operators in subspaces and the eta invariant},
  institution = {Institut f{\"u}r Mathematik},
  series    = {Preprint},
  number    = {(1999) 14},
  year    = {2008},
}