1. The index of isolated critical points and solutions of elliptic equations in the plane,;G. Alessandrini;Ann. Scuola Norm. Sup. Pisa Cl. Sci. (4),1992
2. Uniqueness of critical points for semi-linear elliptic problems in convex domains,;J. Arango;Electron. J. Differential Equations,2005
3. Morse theory for analytic functions on surfaces,;J. Arango;J. Geom.,2005
4. "The Theory of Singularities and its Applications,'';V. I. Arnold;Cambridge University Press,1991
5. Stable solutions of semilinear elliptic problems in convex domains,;X. Cabr\'e;Selecta Math. (N.S.),1998