1. [Ba73] H. Bart,Meromorphic opertor valued functions, Thesis, Vrije Universiteit, Amsterdam (1973).
2. [Bo88] Z. Boulmaarouf,The Laffey-West decomposition, Proc. R. Ir. Acad. 88 A (1988), 125?131.
3. [CuZw95] R. F. Curtain and H. J. Zwart,An introduction to infinite-dimensional linear systems theory, Springer, New York, 1995.
4. [FöJa92] K.-H. Förster and K. Jahn,Extremal compressions and perturbations of bounded operators, Proc. Roy. Irish Acad. 92 A (1992), 289?296.
5. [FöKr96] K.-H. Förster and M. Krause,On extremal perturbations of semi-Fredholm operators, Integral Equations Operator Theory 26 (1996), 125?135.