1. X. Carvajal and W. Neves. Operators that achieve the norm. Integral Equations and Operator Theory, 72 (2012), 179–195.
2. B. Chevreau. Personal communications.
3. I. Chalendar. Techniques d’algèbres duales et sous-espaces invariants. (French) [Dual algebra techniques and invariant subspaces] With a preface in Romanian by Bernard Chevreau. Monografii Matematice (Timisoara) [Mathematical Monographs (Timisoara)], 55. Universitatea de Vest din Timisoara, Facultatea de Matematica, Timisoara, (1995), iv+94 pp.
4. M. Fabian, P. Habala, P. Hájek, V.M. Santalucía, J. Pelant and V. Zizler. Functional Analysis and Infinite-Dimensional Geometry, CMS Books in Mathematics, Springer, New York (2001).
5. P.R. Halmos. Introduction to Hilbert space and the theory of spectral multiplicity, Chelsea, New York (1951).