1. Approximationstheorie im Raum C(R);Albinus;Beiträge Anal.,1972
2. Approximation in Metric Linear Spaces;Albinus,1979
3. Applications of Functional Analysis to Approximation Theory;Dkutsch,1978
4. Applications of the Hahn-Banach theorem in approximation theory;Deutsch;SIAM Rev.,1967
5. Linear Operators I;Dunford,1957