1. S. Banach,Théorie des Operations Lineaires, Warsaw, 1932.
2. F. Bohnenblust,Subspaces of l pn spaces, Amer. J. Math.63 (1941) 64–72.
3. M. M. Day,On the basis problem in normed spaces, Proc. A.M.S.13 (1962) 655–658.
4. N. Dunford, and J. Schwartz,Linear Operators (part 1), New York, 1957.
5. A. Dvoretzky,A characterization of Banach spaces isomorphic to inner product spaces Proc. Coll. Convexity, Univ. of Copenhagen, 1966, 61–66.