1. Ando, T.: Operators with a norm condition. Acta Sci. Math. (Szeged) 33, 169–178 (1972)
2. Arias, M.L., Corach, G., Gonzalez, M.C.: Partial isometries in semi-Hilbertian spaces. Linear Algebra Appl. 428(7), 1460–1475 (2008)
3. Arias, M.L., Corach, G., Gonzalez, M.C.: Metric properties of projections in semi-Hilbertian spaces. Integral Equ. Oper. Theory 62(1), 11–28 (2008)
4. Arias, M.L., Corach, G., Gonzalez, M.C.: Lifting properties in operator range. Acta Sci. Math. (Szeged) 75(3–4), 635–653 (2009)
5. Conway, J.B.: A Course in Functional Analysis, 2nd edn. Springer, Berlin (1990)