On semilinear elliptic equations with indefinite nonlinearities

Abstract: "This paper concerns semilinear elliptic equations whose nonlinear term has the form W(x)f(u) where W changes sign. We study the existence of positive solutions and their multiplicity. The important role played by the negative part of W is contained in a condition which is shown to be necessary for homogeneous f. More general existence questions are also discussed."