1. Akhiezer N.I., Glazman I.M.: Theory of Linear Operators in Hilbert Space, vol. II. Ungar Pub. Co., New York (1963)
2. Derkach V.A.: On extensions of the Laguerre operator in indefinite inner product spaces. Mat. Zametki 63, 509–521 (1998) (in Russian)
3. Dijksma A., Kurasov P., Shondin Yu.G.: High order singular rank one perturbations of a positive operator. Integral Equ. Oper. Theory 53, 209–245 (2005)
4. Dijksma A., Langer H., Luger A., Shondin Yu.: Minimal realizations of scalar generalized Nevanlinna functions related to their basic factorization. Oper. Theory Adv. Appl. 154, 69–90 (2004)
5. Dijksma A., Langer H., Shondin Yu.G., Zeinstra C.: Self-adjoint operators with inner singularities and Pontryagin spaces. Oper. Theory Adv. Appl. 118, 105–175 (2000)