[1] A. ALEXIEWICZ W. ORLICZ:
Analytic operations in real Banach spaces. Studia Math. XIV (1953), 57-78.
MR 0062947
[2] E. S. CITLANADZE:
Teoremy suščestvovanija toček minimaksa v prostranstvech Banacha. Trudy Mosk. Mat. Obšč. 2 (1953), 235-274.
MR 0055574
[3] S. FUČÍK J. NEČAS:
Ljusternik-Schnirelman theorem and nonlinear eigenvalue problems. (to appear in Math. Nachr.).
MR 0333863
[4] M. A. KRASNOSELSKIJ: Topological methods in the theory of nonlinear integral equations. Pergamon Press, N. Y. 1964.