P. Korman et al., EXACT MULTIPLICITY RESULTS FOR BOUNDARY-VALUE-PROBLEMS WITH NONLINEARITIES GENERALIZING CUBIC, Proceedings of the Royal Society of Edinburgh. Section A. Mathematics, 126, 1996, pp. 599-616
Using techniques of bifurcation theory we present two exact multiplici
ty results for boundary value problems of the type u ''+lambda f(x,u)=
0 for -L<x<L, u(-L)=u(L)=0. The first result concerns the case when th
e nonlinearity is independent of x and behaves like a cubic in u. The
second one deals with a class of nonlinearities with explicit x depend
ence.