“…Let Ω ⊂ R 2 be a bounded domain with boundary ∂Ω = Γ = 8 i=1 Γ i , where Γ 1 = {0}×[0, 1], Γ 2 = {0}× [1,3], Γ 3 = [0, 1]×{3}, Γ 4 = {1}× [1,3], Γ 5 = [1,5]×{1}, Γ 6 = {5} × [0, 1], Γ 7 = [1,5] × {0} and Γ 8 = [0, 1] × {0}, see Figure 1. Given four real numbers λ 1 , λ 2 , λ 3 and λ 4 , we consider the problem:…”