EN
We prove that a function belonging to a fractional Sobolev space $L^{α,p}(ℝⁿ)$ may be approximated in capacity and norm by smooth functions belonging to $C^{m,λ}(ℝⁿ)$, 0 < m + λ < α. Our results generalize and extend those of [12], [4], [14], and [11].