1. B. Aupetit, A primer on spectral theory, Springer, New York, 1991.
2. J. B. Conway, Functions of one complex variable, Springer, New York, 1978.
3. J. B. Conway, A course in functional analysis, Springer, New York, 1985.
4. R. E. Harte, Fredholm theory relative to a Banach algebra homomorphism, Math. Z. \bf179 (1982), 431–436.
5. R. E. Harte and A. W. Wickstead, Boundaries, hulls and spectral mapping theorems, Math. Proc. R. Ir. Acad. \bf81A(2) (1981), 201–208.