Let $D_1,D_2$ be two simply connected open subsets of $\mathbb{R}^2$. Let's suppose that it's intersection is nonempty and connected. Then $ D_1\cup D_2$ is simply connected. I have no idea how can I do this.
union of two simply connected open , with open and non empty intersection in $R^2$
7
$\begingroup$
real-analysis