1. Berens, H., Hetzelt, L.: Die Metrische Struktur der Sonnen inl ?(n). Aequationes Math.27, 274?287 (1984)
2. Berens, H., Hetzelt, L.: Suns and contractive retracts in the plane (preprint)
3. Brown, A.L.: Chebyshev sets and the shapes of convex bodies. In: Methods of functional analysis in approximation theory. Proceedings of an international conference, Bombay 1985. Micchell, C., Pai, D.V., Limaye, B.V. (eds.) pp. 97?121. Basel, Boston, Stuttgart: Birkh�user 1986
4. Efimov, N.V., Stechkin, S.B.: Some properties of Chebyshev sets. Dokl. Akad. Nauk SSSR (N.S.)118, 17?19 (1958)
5. Eilenberg, S., Montgomery, D.: Fixed point theorems for multivalued transformations. Am. J. Math.68, 221?222 (1946)