1. [1] H. Berestycki, P. L. Lions, and I. A. Peletier, An ODE approach to the existence of positive solutions for semilinear problems in $\mathbbR^N$, Indiana Univ. Math. J. 30 (1981), no. 1, 141–157.
2. [2]1 H. Berestycki and P. L. Lions, Existence d'ondes solitaires dans des problèmes non-linéaires du type Klein-Gordon, C. R. Acad. Sci. Paris Sér. A-B 287 (1978), no. 7, A503–A506.
3. [2]2 H. Berestycki and P. L. Lions, Existence d'ondes solitaires dans des problèmes nonlinéaires du type Klein-Gordon, C. R. Acad. Sci. Paris Sér. A-B 288 (1979), no. 7, A395–A398.
4. [3] T. Cazenave and F. Weissler, Some remarks on the nonlinear Schrödinger equation in the critical case, Nonlinear semigroups, partial differential equations and attractors (Washington, DC, 1987), Lecture Notes in Math., vol. 1394, Springer, Berlin, 1989, pp. 18–29.
5. [4] W. Craig, T. Kappeler, and W. Strauss, preprint.