1. Hutton, C. V., Morrell, J. S., Retherford, J. R.: Approximation numbers and Kolmogoroff diameters of bounded linear operators (submitted to J. Approx. Theory; abstract to appear Bull. Amer. Math. Soc., May, 1974)
2. Lindenstrauss, J., Rosenthal, H. P.: The ?p-spaces. Israel J. Math.7, 325?349 (1969)
3. Mitiagin, B. S., Pelczynski, A.: Nuclear operators and approximative dimension. Int. Math. Congress 366?375 (1966)
4. Pietsch, A.: Einige neue Klassen von kompakten linearen Abbildungen. Revue de Math. Pure et Appl. (Bucharest)8, 423?447 (1963)
5. Pietsch, A.: Nukleare lokalkonvexe Räume. Berlin: Academie-Verlag 1965