@article{BrascheKoshmanenkoNeidhardt1994,
  author    = {Brasche, Johannes F. and Koshmanenko, V. D. and Neidhardt, Hagen},
  title     = {Some new aspects of Krein's extension theory},
  year      = {1994},
  language  = {en}
}
@article{BrascheNeidhardt1994,
  author    = {Brasche, Johannes F. and Neidhardt, Hagen},
  title     = {Some remarks to Krein's extension theory},
  year      = {1994},
  language  = {en}
}