  Let $\Omega\subseteq\mathcal{R}^2$ be a domain, let $X$ be a rearrangement
invariant space and let $f\in W^{1}X(\Omega,\mathcal{R}^2)$ be a homeomorphism
between $\Omega$ and $f(\Omega)$. Then there exists a sequence of
diffeomorphisms $f_k$ converging to $f$ in the space
$W^{1}X(\Omega,\mathcal{R}^2)$.
