Given an open bounded set $D\subset \mathbb R^N$, let $f\in W^{-1,q}(D)$ and let $u$ be a Sobolev function $u\in W_0^{1,p}(D)$ such that $u$ solves the PDE $$ \begin{cases} -\Delta_p u=f\;\text{in $D$}\\ u\in W_0^{1,p}(D) \end{cases} $$

Given $\Omega\subset D$ (which can be assumed open, or quasi open) we can define $P_{\Omega}:W_0^{1,p}(D)\to W_0^{1,p}(\Omega)$, $P_{\Omega}=\mathrm{Proj}_{W_0^{1,p}(\Omega)}$ (the projection of the function onto the subspace $W_0^{1,p}(\Omega)$).

I wish to prove that the function $u_{\Omega}=P_{\Omega}u$ solves the PDE

$$ \begin{cases} -\Delta_p u_{\Omega}=f\;\text{in $\Omega$}\\ u_{\Omega}\in W_0^{1,p}(\Omega) \end{cases} $$

It would suffice if I could find a proof for $f\equiv 1$.