@unpublished{XiaochunSchulze2008,
  author  = {Liu Xiaochun and Bert-Wolfgang Schulze},
  title   = {Boundary value problems in edge representation},
  institution = {Institut f{\"u}r Mathematik},
  series    = {Preprint},
  number    = {(2004) 14},
  year    = {2008},
}