1. Alessandrini, G.: Critical points of solutions of elliptic equations in two variables. Ann. Scuola Norm. Sup. Pisa Cl. Sci. (4) 14(2), 229–256 (1988) (1987)
2. Alessandrini, G.: Critical points of solutions to the $$p$$-Laplace equation in dimension two. Boll. Un. Mat. Ital. A (7) 1(2), 239–246 (1987)
3. Alessandrini, G., Lupo, D., Rosset, E.: Local behavior and geometric properties of solutions to degenerate quasilinear elliptic equations in the plane. Appl. Anal. 50(3–4), 191–215 (1993)
4. Alessandrini, G., Magnanini, R.: The index of isolated critical points and solutions of elliptic equations in the plane. Ann. Scuola Norm. Sup. Pisa Cl. Sci. (4) 19(4), 567–589 (1992)
5. Alessandrini, G., Magnanini, R.: Elliptic equations in divergence form, geometric critical points of solutions, and Stekloff eigenfunctions. SIAM J. Math. Anal. 25(5), 1259–1268 (1994)