1. Allegretto, W.: Postitive solutions and spectral properties of weakly coupled elliptic systems. J. Math. Anal. Appl. (to appear)
2. Allegretto, W.: Sturmian theorems for second order systems. Proc. Am. Math. Soc.94, 291?296 (1985)
3. Allegretto, W., Mingarelli, A.: On the non-existence of positive solutions for a Schrodinger equation with an indefinite weight function. C.R. Math. Rep. Acad. Sci. Canada8, 69?73 (1986)
4. Allegretto, W., Mingarelli, A.: in preparation
5. Atkinson, F.V., Jabon, D.: Indefinite Sturm-Liouville problems. Proceedings of the 1984 Workshop on spectral Theory of Sturm-Liouville Differential Operators, Argonne National Laboratory 1984