Is it possible to construct an embedding $D^4\hookrightarrow S^2\times \mathbb R^2$ such that the projection $D^4\to S^2$ is an open map?
Here $D^n$ denotes closed $n$-ball.
An open map D⁴ → S². It is easy to construct an embedding $D^3\hookrightarrow S^3$ such that its composition with Hopf fibration $f_3:D^3\to S^2$ is open.
Composing $f_3$ with any open map $D^4\to D^3$, one gets an open map $f_4:D^4\to S^2$.
The map $f_3$ is not a projection of embedding $D^3\hookrightarrow S^2\times\mathbb R$. (We have $f_3^{-1}(p)=S^1$ for some $p\in S^2$ and $S^1$ can not be embedded in $\mathbb R$.)
I still do not understand if one can present $f_4$ as a projection of an embedding $D^4\hookrightarrow S^2\times\mathbb R^2$.