1. Weyl’s theorem for nonnormal operators;Coburn, L. A.;Michigan Math. J.,1966
2. Projections de meilleure approximation continues dans certains espaces de Banach;Fakhoury, Hicham;C. R. Acad. Sci. Paris S\'{e}r. A-B,1973
3. Translations of Mathematical Monographs, Vol. 18;Gohberg, I. C.,1969
4. Best approximation by compact operators;Holmes, Richard B.;Indiana Univ. Math. J.,1971
5. On operators which attain their norm;Lindenstrauss, Joram;Israel J. Math.,1963