Nonlinear analysis and applications, Proc. 7th Int. Conf., Arlington/Tex. 1986, Lect. Notes Pure Appl. Math. 109, 561-566 (1987).
Summary: [For the entire collection see Zbl 0632.00014.]
We prove that if there exists a sub solution , a strict super solution , a strict sub solution , and a super solution for
such that , and , then (1.1)-(1.2) has at least three distinct solutions such that . (Here we write when and This extends the work by H. Amann [SIAM Review 18, 620- 709 (1976; Zbl 0345.47044)] where the case was studied.