EN
We study the existence and multiplicity of positive solutions of the nonlinear fourth order problem
⎧$u^{(4)} = λf(u)$ in (0,1),
⎨
⎩u(0) = a ≥ 0, u'(0) = a' ≥ 0, u(1) = b ≥ 0, u(1) = -b' ≤ 0
The methods employed are upper and lower solutions and degree theory arguments.