SoleCRIS / Asiantuntija - Hassi Seppo Ortamo

Hassi, Seppo; De Snoo, Henk. (2022). Lebesgue type decompositions and Radon–Nikodym derivatives for pairs of bounded linear operators. 88, 469–503. [Päätekijä]

Derkach, Volodymyr; Hassi, Seppo; Malamud, Mark. (2022). Generalized boundary triples, II. Some applications of generalized boundary triples and form domain invariant Nevanlinna functions. 295, 1113-1162. [Päätekijä]

Baidiuk, D.; Derkach, V.; Hassi, S.. (2021). Unitary Boundary Pairs for Isometric Operators in Pontryagin Spaces and Generalized Coresolvents. 15. [Päätekijä]

Arlinski, Yu. M.; Hassi, S.. (2021). Representations of closed quadratic forms associated with Stieltjes and inverse Stieltjes holomorphic families of linear relations. 27, 103-129. [Päätekijä]

Behrndt, Jussi; Hassi, Seppo. (2021). Recent Developments in Operator Theory - Contributions in Honor of H.S.V. de Snoo. [Päätekijä]

Hassi, Seppo; Wietsma, Hendrik Luit. (2020). Spectral Decompositions of Selfadjoint Relations in Pontryagin Spaces and Factorizations of Generalized Nevanlinna Functions, 515-534. [Päätekijä]

Hassi, S.; Labrousse, J.-Ph.; de Snoo, H.S.V.. (2020). Selfadjoint extensions of relations whose domain and range are orthogonal. 26, 39-62. [Päätekijä]

Hassi, Seppo; Labrousse, Jean-Philippe; de Snoo, Henk. (2020). Operational calculus for rows, columns, and blocks of linear relations. 5, 1193–1228. [Päätekijä]

Derkach, Volodymyr; Hassi, Seppo; Malamud, Mark. (2020). Generalized boundary triples, I. Some classes of isometric and unitary boundary pairs and realization problems for subclasses of Nevanlinna functions. 293, 1278-1327. [Päätekijä]

Behrndt, Jussi; Hassi, Seppo; de Snoo, Henk. (2020). Boundary value problems, Weyl functions, and differential operators. [Päätekijä]

Hassi, Seppo; de Snoo, H. S. V.. (2020). A Class of Sectorial Relations and the Associated Closed Forms, 493-514. [Päätekijä]

Arlinskiĭ, Yury; Hassi, Seppo. (2019). Stieltjes and inverse Stieltjes holomorphic families of linear relations and their representations. Online 20 Dec 2019, 1-33. [Päätekijä]

Arlinskiĭ, Yuri; Hassi, Seppo. (2019). Holomorphic operator-valued functions generated by passive selfadjoint systems, 1-42. [Päätekijä]

Hassi, Seppo; Sandovici, Adrian; de Snoo, Henk. (2019). Factorized sectorial relations, their maximal-sectorial extensions, and form sums. 13, 538-564. [Päätekijä]

Hassi, Seppo; de Snoo, Henk; Winkler, Henrik. (2018). Limit Properties of Eigenvalues in Spectral Gaps, 335-355. [Päätekijä]

Hassi, Seppo; Sebestyén, Zoltán; de Snoo, Henk. (2018). Lebesgue type decompositions for linear relations and Ando's uniqueness criterion. 84, 465-507. [Päätekijä]

Hassi, Seppo; Möller, Manfred; de Snoo, Henk. (2017). Limit-point/limit-circle classification for Hain-Lüst type equations. Mathematische Nachrichten. 2018: 291, 1-17. [Päätekijä]

Hassi, Seppo; A. Sandovici; H.S.V. de Snoo; H. Winkler. (2017). Extremal maximal sectorial extensions of sectorial relations. 28, 1019-1055. [Päätekijä]

Hassi, Seppo; Wietsma, Hendrik L.. (2016). Minimal realizations of generalized Nevanlinna functions. Opuscula Mathematica. 36, 749-768. [Päätekijä]

Baidiuk, D.; Hassi, S.. (2016). Completion, extension, factorization, and lifting of operators. Mathematische Annalen. 364, 1415-1450. [Tekijä]

Arlinskii, Yuri M.; Hassi, Seppo. (2015). Q-functions and boundary triplets of nonnegative operators, 89-130. [Päätekijä]

Hassi, S.; de Snoo, H.S.V.. (2015). Factorization, majorization, and domination for linear relations. Annales Universitatis Scientiarum Budapestinensis de Rolando Eötvös Nominatae: Sectio Mathematica. 58, 55-72. [Päätekijä]

Arlinskii, Yu.; Hassi, Seppo. (2015). Compressed resolvents of selfadjoint contractive exit space extensions and holomorphic operator-valued functions associated with them. Methods of Functional Analysis and Topology. 21, 199-224. [Päätekijä]

S. Hassi, and H.L. Wietsma. (2014). Products of generalized Nevanlinna functions with symmetric rational functions. 266, 3321-3376. [Päätekijä]

S. Hassi, H.S.V. de Snoo, and F.H. Szafraniec. (2014). Normal intermediate extensions of symmetric relations. Acta Universitatis Szegediensis. Acta Scientiarum Mathematicarum. 80, 195-232. [Päätekijä]

Fleige, A.; Hassi, S.; de Snoo, H.S.V. ; Winkler, H.. (2014). Non-semi-bounded closed symmetric forms associated with a generalized Friedrichs extension. 144, 731-745. [Päätekijä]

J. Behrndt, S. Hassi, H.S.V. de Snoo, H.L. Wietsma. (2014). Antitonicity of the inverse for selfadjoint matrices, operators, and relations. 142, 2783-2796. [Päätekijä]

Seppo Hassi. (2014). A completion problem for an unbounded nonnegative block operator. Kirjassa: Contributions to Mathematics, Statistics, Econometrics, and Finance. Essays in Honour of Professor Seppo Pynnönen. Toim.Knif, Johan; Pape, Bernd. 21-32. [Päätekijä]

Hassi, Seppo; Mark Malamud; Vadim Mogilevskii. (2013). Unitary equivalence of proper extensions of a symmetric operator and the Weyl function. Integral Equations and Operator Theory. 77, 449-487. [Päätekijä]

Hassi, S.; Wietsma, H.L.. (2013). Products of generalized Nevanlinna functions with symmetric rational functions. Mathematics Arxiv. eprint arXiv:1312.7248, 1-44. [Päätekijä]

Hassi, Seppo; Kuzhel, Sergii. (2013). On J-self-adjoint operators with stable C-symmetries. Proceedings of the Royal Society of Edinburgh. Section A. Mathematics. 143, 141-167. [Päätekijä]

Behrndt, Jussi; Hassi, Seppo; de Snoo, Henk; Wietsma, Rudi; Winkler, Henrik. (2013). Linear fractional transformations of Nevanlinna functions associated with a nonnegative operator. Complex analysis and operator theory. 7, 331-362. [Päätekijä]

Derkach, Vladimir; Hassi, Seppo; de Snoo, Henk. (2012). Truncated moment problem in the class of generalized Nevanlinna functions. Mathematische Nachrichten. 285, 1741-1769. [Päätekijä]

Hassi, Seppo; de Snoo Hendrik S.V.; Szafraniec, Franciszek H.. (2012). Operator methods for boundary value problems. Toimitettu julkaisu. Cambridge University Press. [Päätekijä]

Malamud, Mark, Mogilevskii, Vadim; Hassi, Seppo. (2012). On the unitary equivalence of the proper extensions of a Hermitian operator and the Weyl function. Mathematical Notes. 91, 302-307. [Päätekijä]

Hassi, Seppo; Wietsma, Hendrik Luit. (2012). On Calkin's abstract symmetric boundary conditions). Kirjassa: Operator methods for boundary value problems. Toim. Hassi, Seppo; de Snoo Hendrik, S.V.; Szafraniec, Franciszek H.. 3-34. [Päätekijä]

Behrndt, Jussi; Hassi, Seppo, de Snoo, Henk; Wietsma, Rudi. (2012). Limit properties of monotone matrix functions. 436, 935-953. [Päätekijä]

Hassi, Seppo; de Snoo, Hendrik S.V.; Szafraniec, Franciszek H.. (2012). John Williams Calkin: a short biography). Kirjassa: Operator methods for boundary value problems. Toim. Hassi, Seppo; de Snoo, Hendrik S.V.; Szafraniec, Franciszek H.. 1-2. [Päätekijä]

Hassi, Seppo; de Snoo, H.S.V.; Szafraniec, F.H.. (2012). Infinite-dimensional perturbations, maximally nondensely defined symmetric operators, and some matrix representations. Indagationes Mathematicae. 23, 1087-1117. [Päätekijä]

Hassi, Seppo; van der Schaft, Arjan J; de Snoo, Hendrik S.V.; Zwart, Hans J.. (2012). Dirac structures and boundary relations). Kirjassa: Operator methods for boundary value problems. Toim. Hassi, Seppo; de Snoo, Hendrik S.V.; Szafraniec, Franciszek H.. 259-274. [Päätekijä]

Derkach, V.A.; Hassi, Seppo; Malamud, M.M.: de Snoo, Hendrik S.V.. (2012). Boundary triplets and Weyl functions. Recent developments). Kirjassa: Operator methods for boundary value problems. Toim. Hassi, Seppo; de Snoo, Hendrik S.V.; Szafraniec, Franciszek H.. 161-220. [Päätekijä]

Behndt, J.; Hassi, S.; de Snoo, H.S.V.; Wietsma, H.L.. (2011). Square-integrable solutions and Weyl functions for singular canonical systems. 284, 1334-1384. [Päätekijä]

J. Behrndt, S. Hassi, H.S.V. de Snoo, R. Wietsma, and H. Winkler. (2011). Linear fractional transformations of Stieltjes functions. Konferenssijulkaisussa: Proceedings in Applied Mathematics and Mechanics (PAMM). 887-888. [Päätekijä]

J. Behrndt, V. Derkach, S. Hassi, and H.S.V. de Snoo. (2011). A Realization theorem for generalized Nevanlinna families. Operators and Matrices. 5, 679-706. [Päätekijä]

V.A. Derkach, S. Hassi, and H.S.V. de Snoo. (2010). Truncated moment problem in the class of generalized Nevanlinna functions. Mathematics ArXiv, 1--30. [Päätekijä]

Fleige, A.; Hassi, S.; de Snoo,H.S.V. ; Winkler, H.. (2010). Sesquilinear forms corresponding to a non-semibounded Sturm-Liouville operator. 140, 291-318. [Päätekijä]

S. Hassi and S. Kuzhel. (2010). On J-self-adjoint operators with stable C-symmetry. Mathematics ArXiv, 1--30. [Päätekijä]

Behrndt, J. ; Hassi, S.; De Snoo, H.S.V., Wietsma, H.L.. (2010). Monotone convergence theorems for semi-bounded operators and forms with applications. Proceedings of the Royal Society of Edinburgh Section A-Mathematics. 140, 927-951. [Päätekijä]

Hassi, S; de Snoo, H; Tsekanovskii, E. (2009). The realization problem for Herglotz-Nevanlinna functions). Kirjassa: Unsolved Problems in Mathematical Systems and Control Theory. Toim. Blondel, Vincent D.; Megretski, Alexandre. 8-13. [Päätekijä]

Hassi, S; Oridoroga, L. (2009). Theorem of completeness for a Dirac-type operator with generalized lambda-depending boundary conditions. Integral Equations and Operator Theory. 64, 357-379. [Päätekijä]

Arlinskii, Yury M; Hassi, Seppo; de Snoo, Henk S. V. (2009). Passive systems with a normal main operator and quasi-selfadjoint systems. Complex Analysis and Operator Theory. 3, 19-56. [Päätekijä]

Hassi, S; Kuzhel, S. (2009). On symmetries in the theory of finite rank singular perturbations. Journal of Functional Analysis. 256, 777-809. [Päätekijä]

Hassi, S; Sebestyen, Z; Snoo de H.S.V.. (2009). Lebesgue type decompositions for nonnegative forms. Journal of Functional Analysis. 257, 3858-3894. [Päätekijä]

S. Hassi;Z. Sebestyen;and H.S.V. de Snoo. (2009). Domain and range descriptions for adjoint relations, and parallel sums and differences of forms. Operator Theory: Advances and Applications. 198, 211-227. [Päätekijä]

S. Hassi;H.S.V. de Snoo;and F.H. Szafraniec. (2009). Componentwise and Cartesian decompositions of linear relations. Dissertationes Mathematicae. 465, 4-58. [Päätekijä]

J. Behrndt;S. Hassi;and H.S.V. de Snoo. (2009). Boundary relations, unitary colligations, and functional models. Complex Analysis and Operator Theory. 3, 57-98. [Päätekijä]

V.A. Derkach;S. Hassi;M.M. Malamud;and H.S.V. de Snoo. (2009). Boundary relations and generalized resolvents of symmetric operators. Russian Journal of Mathematical Physics. 16, 17-60. [Päätekijä]

S. Hassi and S. Kuzhel. (2008). Symmetries in the theory of finite rank singular perturbations. [Päätekijä]

S. Hassi;A. Sandovici;H.S.V. de Snoo;and H. Winkler. (2008). One-dimensional perturbations, asymptotic expansions, and spectral gaps. Operator Theory: Advances and Applications. 188, 149--173. [Päätekijä]

J. Behrndt;S. Hassi;and H.S.V. de Snoo. (2008). Functional models for Nevanlinna families. Opuscula Mathematica. 28, 233-245. [Päätekijä]

Yu.Arlinskii;S. Hassi;and H.S.V. de Snoo. (2007). Passive systems with a normal main operator and quasi-selfadjoint systems. [Päätekijä]

Yu. Arlinskiu{i};S. Hassi;and H.S.V. de Snoo. (2007). Parametrization of contractive block-operator matrices and passive discrete-time systems. Complex Analysis and Operator Theory. 1, 211--233. [Päätekijä]

S. Hassi;H.S.V. de Snoo;and H. Winkler. (2007). On exceptional extensions close to the generalized Friedrichs extension of symmetric operators. Operator Theory: Advances and Applications. 175, 111-120. [Päätekijä]

S. Hassi;H.S.V. de Snoo;A.E. Sterk;and H. Winkler. (2007). Finite-dimensional graph perturbations of selfadjoint Sturm-Liouville operators, 205-228. [Päätekijä]

S. Hassi;A. Sandovici;H.S.V. de Snoo;and H. Winkler. (2007). Extremal extensions for the sum of nonnegative selfadjoint relations. Proceedings of the American Mathematical Society. 135, 3193-3204. [Päätekijä]

Derkach V.A. ;S. Hassi;and H.S.V. de Snoo. (2007). Asymptotic expansions of generalized Nevanlinna functions and their spectral properties. Operator Theory: Advances and Applications. 175, 51-88. [Päätekijä]

S. Hassi;A. Sandovici;H.S.V. de Snoo;and H. Winkler. (2007). A general factorization approach to the extension theory of nonnegative operators and relations. Journal of Operator Theory. 58, 351-386. [Päätekijä]

S. Hassi;Z. Sebestyen;H.S.V. de Snoo;and F.H. Szafraniec. (2007). A canonical decomposition for linear operators and linear relations. Acta Mathematica Hungarica. 115, 281-307. [Päätekijä]

Yu. Arlinskii;S. Hassi;and H.S.V. de Snoo. (2006). Parametrization of contractive block-operator matrices and passive discrete-time systems. [Päätekijä]

S. Hassi and S. Kuzhel. (2006). On symmetries in the theory of singular perturbations. [Päätekijä]

S. Hassi;H.S.V. de Snoo;A. Sterk;and H. Winkler. (2006). Non-standard boundary conditions for a class of Sturm-Liouville problems. Revue Roumaine de Mathematiques Pures et Appliquees/Romanian Journal of Pure and Applied Mathematics.. 51, 641-653. [Päätekijä]

S. Hassi and A. Luger. (2006). Generalized zeros and poles of N_kappa-functions: On the underlying spectral structure. Methods of Functional Analysis and Topology. 12, 131-150. [Päätekijä]

S. Hassi;A. Sandovici;H.S.V. de Snoo;and H. Winkler. (2006). Form sums of nonnegative selfadjoint operators. Acta Mathematica Hungarica. 111, 81-105. [Päätekijä]

S. Hassi and L.L. Oridoroga. (2006). Completeness and Riesz basis property of systems of eigenfunctions and associated functions of Dirac-type operators with boundary conditions depending on the spectral parameter. Mathematical Notes. 79, 589-593. [Päätekijä]

V.A. Derkach;S. Hassi;M.M. Malamud;and H.S.V. de Snoo. (2006). Boundary relations and their Weyl families. Transactions of the American Mathematical Society. 358, 5351-5400. [Päätekijä]

V.A. Derkach;S. Hassi;M.M. Malamud;and H.S.V. de Snoo. (2006). Boundary relations and generalized resolvents of symmetric operators. [Päätekijä]

Belyi, Sergey; Hassi, Seppo; de Snoo, Henk; Tsekanovskii, Eduard. (2006). A general realization theorem for matrix-valued Herglotz-Nevanlinna functions. 419, 331-358. [Päätekijä]

S. Hassi;M. Möller;and H.S.V. de Snoo. (2006). A class of Nevanlinna functions associated with Sturm-Liouville operators. Proceedings of the American Mathematical Society. 134, 2885-2893. [Päätekijä]

S. Hassi;Z. Sebestyen;H.S.V. de Snoo;F.H. Szafraniec. (2006). A canonical decomposition for linear operators and linear relations. [Päätekijä]

Hassi Seppo and Karabash Ilia. (2005). Similarity between $J$-self-adjoint Sturm-Liouville operators with an operator potential and self-adjoint operators. Mathematical Notes. 78, 581-585. [Päätekijä]

Arlinskii Yury;Hassi Seppo;de Snoo Henk. (2005). Q-functions of quasi-selfadjoint contractions. Kirjassa. Toim.. 1-31. [Päätekijä]

Yu. Arlinskii;S. Hassi;H.S.V. de Snoo. (2005). Q-functions of quasi-selfadjoint contractions. Operator Theory: Advances and Applications. 163, 23-54. [Päätekijä]

Arlinskii Yury;Hassi Seppo;de Snoo Henk. (2005). Q-functions of Hermitian contractions of Krein-Ovcharenko type. Integral Equations and Operator Theory. 53, 153-189. [Päätekijä]

Hassi Seppo;Keränen Veikko;Källman Carl-Gustav;Laaksonen Matti;Linna Matti (Eds). (2005). Proceedings of the Algorithmic Information Theory Conference, Vaasa 2005. University of Vaasa: Vaasa, Finland. [Päätekijä]

Hassi Seppo;Sebesty'en Zoltan and de Snoo Henk. (2005). On the nonnegativity of operator products. Acta Math. Hungarica. 109, 1-15. [Päätekijä]

Hassi Seppo;Malamud Mark;and Mogilevskii Vadim. (2005). Generalized resolvents and boundary triplets for dual pairs of linear relations. Methods of Functional Analysis and Topology. 11, 170-187. [Päätekijä]

A. Fleige;S. Hassi;H.S.V. de Snoo;and H. Winkler. (2005). Generalized Friedrichs extensions associated with interface conditions for Sturm-Liouville operators. Operator Theory: Advances and Applications. 163, 135-145. [Päätekijä]

Hassi Seppo;Sandovici Adrian;de Snoo Henk;and Winkler Henrik. (2005). Extremal extensions of nonnegative linear relations. Konferenssijulkaisussa: Proceedings of the Algorithmic Information Theory Conference. 57-66. [Päätekijä]

Derkach Vladimir;Hassi Seppo;Malamud Mark;and de Snoo Henk. (2005). Boundary relations and orthogonal coupling of symmetric operators. Konferenssijulkaisussa: Proceedings of the Algorithmic Information Theory Conference. 41-56. [Päätekijä]

Derkach Vladimir;Hassi Seppo;and de Snoo Henk. (2005). Asymptotic expansions of generalized Nevanlinna functions and their spectral properties. Kirjassa. Toim.. 1-38. [Päätekijä]

Derkach Vladimir;Hassi Seppo;and de Snoo Henk. (2005). A factorization model for the generalized Friedrichs extension in a Pontryagin space. Operator Theory: Advances and Applications. 162, 117-133. [Päätekijä]

Hassi, Seppo; Möller, Manfred; de Snoo, Henk. (2004). Singular Sturm-Liouville problems whose coefficients depend rationally on the eigenvalue parameter.. 295, 258-275. [Päätekijä]

Derkach;Vladimir;Seppo Hassi;and Henk de Snoo. (2004). Singular perturbations as range perturbations in a Pontryagin space.. Oper. Theory Adv. Appl.. 154, 51-68. [Päätekijä]

Hassi;Seppo and Ilia Karabash. (2004). Similarity of J-selfadjoint Sturm-Liouville operators with an operator potential to selfadjoint ones.. Konferenssijulkaisussa. 44-46. [Päätekijä]

Hassi;Seppo. (2004). On the Friedrichs and the Krein-von Neumann extension of nonnegative relations. Kirjassa: Contributions to Management Science, Mathematics and Modelling. Essays in Honour of Professor Ilkka Virtanen.. Toim.Laaksonen;Matti and Seppo Pynnönen (eds). 37-54. [Päätekijä]

Hassi;Seppo;Mark Malamud;and Henk de Snoo. (2004). On Krein's extension theory of nonnegative operators.. Math. Nachr.. 274/275, 40-73. [Päätekijä]

Derkach;Vladimir;Seppo Hassi;Mark Malamud;and Henk de Snoo. (2004). Boundary relations and the Weyl families.. Rus. Doklady Acad. Sci.. 399, 151-156. [Päätekijä]

Derkach;Vladimir;Seppo Hassi;Mark Malamud;and Henk de Snoo. (2004). Boundary relations and their Weyl families. Kirjassa. Toim.. 1-54. [Päätekijä]

Hassi Seppo;Möller Manfred;de Snoo Henk. (2003). Sturm-Liouville operators and their spectral functions. Journal of Mathematical Analysis and Applications. 282, 584-602. [Päätekijä]

Derkach Vladimir;Hassi Seppo;de Snoo Henk. (2003). Singular perturbations of selfadjoint operators. Mathematical Physics, Analysis and Geometry. 6, 349-384. [Päätekijä]

Derkach Vladimir;Hassi Seppo;de Snoo Henk. (2003). Singular perturbations as range perturbations in a Pontryagin space. Kirjassa. Toim.. [Päätekijä]

Arlinskii Yury;Hassi Seppo;de Snoo Henk. (2003). Q-functions of Hermitian contractions of Krein-Ovcharenko type. Kirjassa. Toim.. [Päätekijä]

Arlinskii Yury;Hassi Seppo;de Snoo Henk;and Tsekanovskii Eduard. (2003). One-dimensional perturbations of selfadjoint operators with finite or discrete spectrum. Contemporary Mathematics. 323, 419-433. [Päätekijä]

Hassi Seppo and Oridoroga Leonid. (2003). Completeness theorems for Dirac-type operators with boundary conditions of general form depending on the spectral parameter. Mathematical Notes. 74, 302-307. [Päätekijä]

Derkach Vladimir;Hassi Seppo. (2003). A reproducing kernel space model for N_k-functions. Proceedings of the American Mathematical Society. 131. [Päätekijä]

Hassi Seppo;Oridoroga Leonid. (2002). Theorem of completeness for a Dirac type operator with generalized $lambda$-depending boundary conditions. Konferenssijulkaisussa. [Päätekijä]

Derkach Vladimir;Hassi Seppo;de Snoo Henk. (2002). Singular perturbations of selfadjoint operators. Kirjassa. Toim.. [Päätekijä]

Hassi Seppo;de Snoo Henk;Tsekanovskii Eduard. (2002). Realizations of Herglotz-Nevanlinna functions via F-systems. Oper. Theory Adv. Appl.. 132, 183-198. [Päätekijä]

Derkach, Vladimir; Hassi, Seppo; de Snoo, Henk. (2002). Rank one perturbations in a Pontryagin space with one negative square. 188, 317-349. [Päätekijä]

Belyi S.;Hassi Seppo;de Snoo H.S.V.;Tsekanovskii E.R.. (2002). On the realization of inverse Stieltjes functions. Konferenssijulkaisussa: Electronic Proceedings of 15th International Symposium on the Mathematical Theory of Networks and Systems. 1-11. [Päätekijä]

Hassi Seppo;Malamud Mark;de Snoo Henk. (2002). On Krein's extension theory of nonnegative operators. Kirjassa. Toim.. [Päätekijä]

Hassi Seppo. (2002). Matematiikan tutkiminen ja soveltaminen. 5-7. [Päätekijä]

Hassi Seppo;Möller Manfred;de Snoo Henk. (2002). Differential operators and spectral functions. Konferenssijulkaisussa. 313-322. [Päätekijä]

Derkach Vladimir;Hassi Seppo;Malamud Mark;de Snoo Henk. (2001). Weyl functions and intermediate extensions of symmetric operators. Reports Nat. Acad. Sci. Ukraine (Dopov. Nats. Akad. Nauk. Ukraini). 10, 33-39. [Päätekijä]

Derkach Vladimir;Hassi Seppo;de Snoo Henk. (2001). Singular perturbations of selfadjoint operators and their operator models. [Päätekijä]

Hassi Seppo. (2001). Singular perturbations of selfadjoint operators, 14-16. [Päätekijä]

Derkach Vladimir;Hassi Seppo;de Snoo Henk. (2001). Operator models associated with singular perturbations. Methods of Functional Analysis and Topology. 7, 1-21. [Päätekijä]

Arlinskii Yu.M.;Hassi Seppo;Sebestyen Z.;de Snoo Henk. (2001). On the class of extremal extensions of a nonnegative operator. Operator Theory Advances and Applications. 127, 41-81. [Päätekijä]

Hassi Seppo;de Snoo Henk;Tsekanovskii Eduard. (2001). On commutative and noncommutative representations of matrix-valued Herglotz-Nevanlinna functions. Applicable Analysis. 77, 135-147. [Päätekijä]

Hassi Seppo. (2001). Model for N_{kappa}-functions, 37. [Päätekijä]

Derkach Vladimir;Hassi Seppo;de Snoo Henk. (2001). Generalized Nevanlinna functions with polynomial asymptotic behaviour at infinity and regular perturbations. Operator Theory Advances and Applications. 122, 169-189. [Päätekijä]

Hassi Seppo;de Snoo Henk;Tsekanovskii Eduard. (2001). An addendum to the multiplication and factorization theorems of Brodskii-Livsic-Potapov. Applicable Analysis. 77, 125-133. [Päätekijä]