English

Two-point distortion theorems and the Schwarzian derivatives of meromorphic functions

Complex Variables 2018-03-28 v2

Abstract

For a meromorphic function ff in the unit disk U={z:  z<1}U=\{z:\;|z|<1\} and arbitrary points z1,z2z_1,z_2 in UU distinct from the poles of ff, a sharp upper bound on the product f(z1)f(z2)|f'(z_1)f'(z_2)| is established. Further, we prove a sharp distortion theorem involving the derivatives f(z1)f'(z_1), f(z2)f'(z_2) and the Schwarzian derivatives Sf(z1)S_f(z_1), Sf(z2)S_f(z_2) for z1,z2Uz_1,z_2\in U. Both estimates hold true under some geometric restrictions on the image f(U)f(U).

Keywords

Cite

@article{arxiv.1803.04619,
  title  = {Two-point distortion theorems and the Schwarzian derivatives of meromorphic functions},
  author = {V. Dubinin},
  journal= {arXiv preprint arXiv:1803.04619},
  year   = {2018}
}

Comments

Substantial style improvement; a number of points better explained; language editing; 8 pages