1. Sulle equazioni ellittiche del secondo ordine a coefficienti continui
2. and : Elliptic Partial Differential Equations of Second Order, 2nd ed. Springer-Verlag, Berlin, 1983
3. , and : Inequalities, Cambridge Univ. Press, Cambridge, 1964
4. and : Non-Homogeneous Boundary Value Problems and Applications, I, Springer-Verlag, Berlin, 1972