@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{BrascheNeidhardt1994, author = {Brasche, Johannes F. and Neidhardt, Hagen}, title = {Some remarks to Krein's extension theory}, year = {1994}, language = {en} } @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} }