@book{NeidhardtZagrebnov1994,
  author    = {Neidhardt, Hagen and Zagrebnov, Valentin A.},
  title     = {Mathematical results in quantum mechanics : international conference in Blossin (Germany), May 17 - 21, 1993},
  series = {Operator Theory},
  volume    = {70},
  journal   = {Operator Theory},
  editor    = {Demuth, Michael and Exner, Pavel},
  publisher = {Birkh{\"a}user},
  address   = {Basel},
  pages     = {X, 356 S.},
  year      = {1994},
  language  = {en}
}
@article{NeidhardtZagrebnov1994,
  author    = {Neidhardt, Hagen and Zagrebnov, Valentin A.},
  title     = {Singular perturbations, regularization and extension theory},
  year      = {1994},
  language  = {en}
}
@article{NeidhardtZagrebnov1996,
  author    = {Neidhardt, Hagen and Zagrebnov, Valentin A.},
  title     = {Towards the right Hamiltonians for singular perturbations via regularization and extension theory},
  year      = {1996},
  language  = {en}
}
@article{NeidhardtZagrebnov1997,
  author    = {Neidhardt, Hagen and Zagrebnov, Valentin A.},
  title     = {On the right Hamiltonian for the singular perturbations : general theory},
  year      = {1997},
  language  = {en}
}
@article{NeidhardtZagrebnov1997,
  author    = {Neidhardt, Hagen and Zagrebnov, Valentin A.},
  title     = {Fractional powers of self-adjoint operators and Trotter-Kato product formula},
  year      = {1997},
  language  = {en}
}
@article{NeidhardtZagrebnov1998,
  author    = {Neidhardt, Hagen and Zagrebnov, Valentin A.},
  title     = {On operator-norm convergence of the Trotter-Kato product formula},
  year      = {1998},
  language  = {en}
}
@article{NeidhardtZagrebnov1998,
  author    = {Neidhardt, Hagen and Zagrebnov, Valentin A.},
  title     = {Does each symmetric operator have a stability domain?},
  year      = {1998},
  language  = {en}
}
@article{NeidhardtZagrebnov1998,
  author    = {Neidhardt, Hagen and Zagrebnov, Valentin A.},
  title     = {On error estimates for Trotter-Product formulas.},
  year      = {1998},
  language  = {en}
}
@article{NeidhardtZagrebnov1998,
  author    = {Neidhardt, Hagen and Zagrebnov, Valentin A.},
  title     = {On semibounded restrictions of selfadjoint operators},
  year      = {1998},
  language  = {en}
}
@article{NeidhardtZagrebnov1998,
  author    = {Neidhardt, Hagen and Zagrebnov, Valentin A.},
  title     = {Trotter-Kato product formula and symmetrically-normed ideals},
  year      = {1998},
  language  = {en}
}
@article{NeidhardtZagrebnov1999,
  author    = {Neidhardt, Hagen and Zagrebnov, Valentin A.},
  title     = {Trotter-Kato product formula and operator-norm convergence},
  year      = {1999},
  language  = {en}
}