1. J. Von Neumann, Eine Spectraltheorie für allgemeine Operatoren eines unitären Raumes, Math Nachr 4 (1951) 258–281.
2. S. Fisher, The convex hull of finite Blashke products, Bull A.M.S. 74 (1968) 1128–1129.
3. B. Sz-Nagy and C. Foias, Harmonic Analysis of Operators on Hilbert Space, North-Holland 1970.
4. P. R. Halmos, Shifts on Hilbert Space, J. reine angew Math 208 (1961) 102–112.
5. S. W. Drury, A Generalization of Von Neumann’s inequality to the complex ball, Proc A.M.S., 68/3 (1978) 300–304.