1. Amann, H., Fixed point equations and nonlinear eigenvalue problems in Banach spaces, SIAM Rev., 18, 620–709 (1976).
2. Berestycki, H., & P. L. Lions, Existence of stationary states in nonlinear scalar field equations, in Bifurcation Phenomena in Mathematical Physics and Related Topics, ed. by C. Bardos & D. Bessis, D. Reidel Publ. Co.: Doredrecht, Boston, London, (1980).
3. Brezis, H., & L. Swald, Remarks on sublinear elliptic equations, (preprint).
4. Gidas, B., Ni, W. M., & L. Nirenberg, Symmetry of positive solutions of nonlinear elliptic equations in ℝ
n
, Comm. Math. Phys., 68, 209–243 (1975).
5. Hess, P., On multiple positive solutions of nonlinear elliptic eigenvalue problems, Comm. P.D.E., 6, 951–961 (1981).