[1] C. BERGE: Topological space. McMillan, New York, 1963.

[2] M. S. BRODSKII, D. P. MILMAN: On the center of a convex set. Dokl. Akad. Nauk SSSR (N.S.) 59 (1948), 837-840. MR 0024073

[3] F. E. BROWDER: Nonexpansive nonlinear operators in a Banach space. Proc. Nat. Acad. Sci. U.S.A. 54 (1965), 1041-1044. MR 0187120 | Zbl 0128.35801

[4] J. DANEŠ: Generalized concentrative mappings and their fixed points. Comment. Math. Univ. Carolinae 11 (1970), 115-136. MR 0263063

[5] G. DARBO: Punti uniti trasformazioni a codomino noncompatto. Rend. Sem. Mat. Univ. Padova 24 (1955), 84-92. MR 0070164

[6] D. GÖHDE: Zum Prinzip der kontraktiven Abbildung. Math. Nachrichten 30 (1965), 251-258. MR 0190718

[7] L. S. GOLDŠTEIN I. C. GOHBERG, and A. S. MARKUS: On some properties of linear boonded operators in connection with their q-norms. (Russian). Uč. Zap. Kišinev. un-ta 29 (1957), 29-36.

[8] L. S. GOLDŠTEIN, A. S. MARKUS: On a measure of non-compactness of bounded sets and linear operators. Issled. po Algebre i Matem. Analizu, Kišinev (Russian), 1965.

[9] J. L. KELLEY: General Topology. Van Nostrand, 1955. MR 0070144 | Zbl 0066.16604

[10] W. A. KIRK: A fixed point theorem for mappings which do not increase distance. Amer. Math. Monthly 72 (1965), 1004-1006. MR 0189009

[11] K. KURATOWSKI: Sur les espaces complets. Fundamenta Mathematicae 15 (1930), 300-309.

[12] B. N. SADOVSKII: A fixed point principle. Functional Anal. and Appl. l (1967), 151-153. MR 0211302