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3. G. B. Keller and S. Antman, Branching Theory and Nonlinear Eigenvalue Problems [Russian translation] Mir, Moscow 1979.
4. J. Ize, “Bifurcation theory for Fredholm operators,” Mem. AMS, 7, 174 (1976).
5. V. M. Krasnosel’skii, “Investigation of small solutions of one class of nonlinear operator equations,” Dokl. Akad. Nauk SSSR, 180, No. 1, 22–24 (1966).