1. T. Ando and K. Nishio, Positive selfadjoint extensions of positive symmetric operators, Tôhoku Math. J., 22 (1970), 65–75.
2. Oper. Theory Adv. Appl.;Y. M. Arlinskiĭ,2001
3. Y. M. Arlinskiĭ and E. R. Tsekanovskiĭ, Quasi selfadjoint contractive extensions of Hermitian contractions, Teor. Funkts., Funkts. Anal. Prilozhen, 50 (1988), 9–16.
4. S. Banach, Théorie des opérations linéaires, Éditions Jacques Gabay (Sceaux, 1993), Reprint of the 1932 original.
5. A. Ben-Israel and T. N. E. Greville, Generalized Inverses. Theory and Applications, Springer (New York, 2003).