1. L. Nirenberg, Topics in Nonlinear Functional Analysis, Courant Institute of Mathematical Sciences, New York University Press, New York (1974).
2. M. M. Vainberg and V. A. Trenogin, Ramification Theory of Solutions of Nonlinear Equations [in Russian], Nauka, Moscow (1969).
3. B. V. Loginov, Bifurcation Theory for Nonlinear Equations under the Conditions of Group Invariance [in Russian], FAN, Tashkent (1985).
4. A. A. Boichuk and A. M. Samoilenko, Generalized Inverse Operators and Fredholm Boundary-Value Problems, VSP, Utrecht (2004).
5. J. Nash, “The imbedding problem for Riemannian manifolds,” Ann. Math., 63, 20–63 (1956).