She quantitative version of the Kado theorem

N. A. Shirokov

Zapiski Nauchnykh Seminarov POMI, Investigations on linear operators and function theory. Part XVI, Tome 157 (1987), pp. 103-112

Résumé

The main aim of the paper is to prove the following result. Theorem. Let $\Gamma$ be a $k$–quasiconformal circle, $L$ a Jordan curve (not necessarily quasiconformal). Suppose that $f$ maps $\operatorname{ext} L$ onto $\operatorname{ext} \Gamma$ quasiconformally and that $f(\infty)=\infty$, $f'(\infty)>0$. Suppose further that there is a horaeomorphism $\chi\colon L\to\Gamma$ such that $$ |\chi(\zeta)-\zeta|\leqslant\varepsilon,\quad\zeta\in\Gamma,\quad0<\varepsilon\leqslant1. $$ Then there exist numbers $\alpha=\alpha(k)>0$ and $A=A(k)$ such that $$ |f(\chi(\zeta))-\zeta|\leqslant A\varepsilon^\alpha,\quad\zeta\in\Gamma. $$