I am reading a paper in which the authors recall (without proving) the existence and regularity of solutions to this equations $$-\Delta y + y +\nabla p = f \quad \text{ in } \Omega$$ $$\mathrm{div}\, y = 0 \quad\text{ in }\Omega$$ $$y\cdot n=0,\quad (n\cdot Dy)\cdot \tau=0\quad \text{ in } \Gamma$$ where, $\Omega \subset \mathbb{R}^2$ is a bounded domain with sufficiently smooth boundary $\Gamma$, $n$ and $\tau$ are the unit normal and tangent vectors to the boundary $\Gamma$, $Dy=\frac{1}{2}(\nabla y + \nabla y^T)$.
I'd like to know the proof of these results and maybe more regularities of solutions to this equations. Could you show me some books or papers in which I can find the answer? Many thanks!