(a) Show that there exists no bijective map $f : \mathbb { R } ^ { 2 } \rightarrow \mathbb { R } ^ { 3 }$ such that $f$ and $f ^ { - 1 }$ are differentiable.\\
(b) Let $f : \mathbb { R } ^ { m } \rightarrow \mathbb { R } ^ { n }$ be a differentiable map such that the derivative $D f ( x )$ is surjective for all $x$. Is $f$ surjective?