Butzer, P. L. e., Butzer, P. L., & Szokefalvi-Nagy, B. (1969). Abstract spaces and approximation: Abstrakte R�ume und Approximation. Proceedings of the conference held at the Mathematical Research Institute at Oberwolfach, Black Forest, July 18-27, 1968. Birkh�user.

Butzer, P. L. ed, Paul Leo Butzer, a Bela Szokefalvi-Nagy. Abstract Spaces and Approximation: Abstrakte R�ume Und Approximation. Proceedings of the Conference Held at the Mathematical Research Institute at Oberwolfach, Black Forest, July 18-27, 1968. Basel, Stuttgart: Birkh�user, 1969.

Butzer, P. L. ed, et al. Abstract Spaces and Approximation: Abstrakte R�ume Und Approximation. Proceedings of the Conference Held at the Mathematical Research Institute at Oberwolfach, Black Forest, July 18-27, 1968. Birkh�user, 1969.