1. A generalization of Sturm's separation theorem;Allegretto,1970
2. Oscillation criteria for fourth order elliptic operators;Allegretto;Boll. Un. Mat. Ital.,1970
3. Eigenvalue comparison and oscillation criteria for elliptic operators;Allegretto;J. London Math. Soc.,1971
4. A Comparison theorem for nonlinear operators;Allegretto;Ann. Scuola Norm. Sup. Pisa,1971
5. Oscillation criteria for quasilinear equations;Allegretto;Canad. J. Math.,1974