1. R. A. Adams,Sobolev spaces, Academic Press, New York-San Francisco-London, 1975.
2. J. Agler, E. Franks and D. A. Herrero. Spectral pictures of operators quasisimilar to the unilateral shift, J. Reine und Angewandte Mathematik,422(1991), 1?20.
3. F. A. Al-Musallam, An upper estimate for the distance to the essentiallyG 1 operators, Ph. D. dissertation, Arizona State University (1989).
4. J. H. Anderson, On normal derivations, Proc. Amer. Math. Soc.38 (1973), 135?140
5. Research Notes in Math.;C. Apostol,1984