Let $\lambda \in \mathbb{R}^*$ and $(x_0, y_0) \in \mathbb{R}^2$ be fixed. We define:
$$\Omega_{x_0, y_0, \lambda} = \left\{ \lambda(x,y) + (x_0, y_0) \mid (x,y) \in \Omega \right\}$$
Let $g : \Omega_{x_0, y_0, \lambda} \rightarrow \mathbb{R}$ be a harmonic application.
Show that the application $(x,y) \mapsto g\left(\lambda(x,y) + (x_0, y_0)\right)$ is harmonic on $\Omega$.