Bifurcation theory for a class of second order differential equations

We consider positive solutions of the nonlinear two point boundary value problem u‘‘+λf(u)=0, u(-1)=u(1)=0 , f(u)=u(u-a)(u-b)(u-c)(1-u), 0, depending on a parameter λ. Each solution u(x) is even function, and it is uniquely identified by α=u(0). We will prove, using delicate integral estimates that α=b,1 are not bifurcations points. We explore and prove a series of properties which restrict the location of a bifurcation point by studying the change of concavity of the graph of f and the points where the rays from 0 and b touche the graph of f.