Solvability of the Neumann problem for elliptic equations in chord-arc domains with very big pieces of good superdomains

Let $\Omega \subset \mathbb{R}^{n+1}$ be a bounded chord-arc domain, let $\mathcal L=-{\rm div} A\nabla$ be an elliptic operator in $\Omega$ associated with a matrix $A$ having Dini mean oscillation coefficients, and let $1<p\leq 2$.

In this paper we show that if the regularity problem for $\mathcal L$ is solvable in $L^q$ for some $q>p$ in $\Omega$, $\partial \Omega$ supports a weak $p$-Poincaré inequality, and $\Omega$ has very big pieces of superdomains for which the Neumann problem for $\mathcal L$ is solvable uniformly in $L^q$, then the Neumann problem for $\mathcal L$ is solvable in $L^p$ in $\Omega$.