Let Ω be a bounded open set in R n with C 2,α boundary, n ≥ 2, 0 < α < 1, D 1 and D 2 be two bounded strictly convex open subsets in Ω with C 2,α boundaries which are ε apart and far away from ∂Ω, i.e.where κ 0 , r 0 > 0 are universal constants independent of ε. We denoteGiven ϕ ∈ C 2 (∂Ω), consider the following scalar equation with Dirichlet boundary condition: