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Variational Methods for the Study of Nonlinear Operators. (Russian), Moscow 1956 (English translation: Holden-Day, San Francisco, 1964).
MR 0176364
[2] M. A. KRASNOSELSKIJ: Topological Methods in the Theory of Nonlinear Integral Equations. (Russian), Moscow 1956 (English translation: New York, Pergamon Press, 1964).
[3] J. E. BJÖRK:
On Extension of Lipschitz functions. Arkiv för Math. 7 (1968), 513-515.
MR 0239424