1. E. Bishop and R. R. Phelps,The support functionals of a convex set, Proc. Sympos. Pure Math., Vol. 7, Amer. Math. Soc., Providence, R. I. 1962, 27–35.
2. F. F. Bonsall and J. Duncan,Numerical range, Lecture Notes of the London Math. Soc. 2 (1971), Cambridge, England.
3. F. F. Bonsall, B. E. Cain and H. Schneider,The numerical range of a continuous mapping of a normed space, Aequationes Math.2 (1968), 86–93.
4. D. F. Cudia,The geometry of Banach spaces, Smoothness, Trans. Amer. Math. Soc.110 (1964), 284–314.
5. M. M. Day,Normed Linear Spaces, Academic Press, New York, 1962.