“…By Sard's theorem, we may assume that Γ ǫ is a regular boundary of Ω ǫ , namely, Γ ǫ has dimension n − 1, Γ ǫ ∈ C 4 and u γ = |Du| > 0 on Γ ǫ , where γ is the unit interior normal vector field to Γ ǫ on Ω ǫ . The estimates up to second order to the approximating Dirichlet problem (1.4) were established for k = n in [12] and for general k under certain assumptions in [13], which depend on ǫ. Based on these estimates, we proved the following existence results to (1.4) in [12,13].…”