# Zorich theorem

In 1967, V.A. Zorich proved the following result for quasi-regular mappings in space: A locally homeomorphic quasi-regular mapping $f : \mathbf{R}^n \rightarrow \mathbf{R}^n$, $n \ge 3$, is, in fact, a homeomorphism of $\mathbf{R}^n$.
This result had been conjectured by M.A. Lavrent'ev in 1938. Note that the exponential function shows that there is no such result for $n=2$. In 1971, O. Martio, S. Rickman and J. Väisälä proved a stronger quantitative result: For $n \ge 3$ and $K > 1$ there exists a number $\psi(n,K) \in (0,1)$ , the radius of injectivity, such that every locally injective $K$-quasi-regular mapping $f : B^n \rightarrow \mathbf{R}^n$, where $B^b = B^n(1)$ and $B^n(r) = \{ x \in \mathbf{R}^n : |x| \le r \}$, for $r > 0$, is injective in $B^n(\psi(n,K))$.