1. Sulle funzioni di variable complessa ui un'area circolari;Boggio;Rend. R. Acad. Torino,1912
2. Über eine nichtlineare Randwertaufgabe bei der Gleichung Δu = 0;Carleman;Math. Z.,1921
3. Nonlinear Sturm-Liouville eigenvalue problems and topological degree;Crandall;J. Math. Mech.,1970
4. A uniqueness criterion for harmonic functions under nonlinear boundary conditions;Cushing;J. Math. Anal. Appl.,1971
5. On a conjecture of Levi-Civita;Cushing;J. Math. Mech.,1970