EN
We prove the existence of at least three solutions to the following fractional boundary value problem:
⎧ $-d/dt (1/2 _0D_t^{-σ} (u'(t)) + 1/2 _tD_T^{-σ} (u'(t))) - λβ(t)f(u(t)) - μγ(t)g(u(t)) = 0$, a.e. t ∈ [0, T],
⎨
⎩ u (0) = u (T) = 0,
where $_0D_t^{-σ}$ and $_tD_T^{-σ}$ are the left and right Riemann-Liouville fractional integrals of order 0 ≤ σ < 1 respectively. The approach is based on a recent three critical points theorem of Ricceri [B. Ricceri, A further refinement of a three critical points theorem, Nonlinear Anal. 74 (2011), 7446-7454].