1. Haim Brezis, Jean-Michel Coron, Louis Nirenberg, “Free vibrations for a nonlinear wave equation and a theorem of P. Rabinowitz”, Comm. Pure Applied Math. 33 (1980), 667–684.
2. Ivar Ekeland, “Convexity methods in Hamiltonian mechanics”, Springer-Verlag.
3. Ivar Ekeland, “Le meilleur des mondes possibles”, Seuil; English translation, “The best of all possible worlds” to appear at Chicago University Press.