Let Ω be a bounded smooth domain in R with N ≥ 2 and 1 < p < ∞. We denote by p∗ the critical exponent for the Sobolev trace immersion given by p∗ = p(N − 1)/(N − p) if p < N and p∗ = ∞ if p ≥ N . For any A ⊂ Ω, which is a smooth open subset, we define the space W 1,p A (Ω) = C ∞ 0 (Ω \A), where the closure is taken in W −norm. By the Sobolev Trace Theorem, there is a compact embedding (1.1) W 1...