On meromorphic univalent functions omitting a disc

The class Σ_b is defined to consist of meromorphic univalent functionsH omitting a disc with the radiusb:H(z)=z+ Σ ₀ ^∞ A _n z ⁻ⁿ ,z>1,H(b)>b ∈ (0, 1). By aid of FitzGerald inequalities the inverse coefficients of odd Σ_b-functions are maximized. The result extends the corresponding estimation, due to Netanyahu and Schober, fromb=0 to the whole interval (0, 1). The author wishes to express her gratitude to Professor O. Tammi for valuable discussions connected with the problem. This work was supported by a grant from the Finnish Ministry of Education.     

Extremal problems in subclasses of univalent functions

Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 41, No. 5, pp. 679–685, May, 1989.     

Distortion theorems for univalent meromorphic functions on an annulus

We apply the capacity and symmetrization methods to distortion theorems for analytic functions in an annulus. We show that the classical Teichmüller estimate for the capacity of a doubly-connected domain yields a series of the already known and new inequalities for univalent functions. In particular, we supplement the results of Grötzsch, Duren, and Huckemann. Using the dissymmetrization of condensers we establish sharp estimates for local distortion and the distortion of level curves in n ≥ 2 symmetric directions. In terms of Robin functions we give an analog of the Nehari inequality: some general distortion theorem for several points taking into account the boundary behavior of the function and describing the cases of equalities. As a corollary we give analogs of some inequalities of Solynin, Pommerenke, and Vasil’ev that were obtained previously for univalent and bounded functions in a disk. We prove a distortion theorem that involves the Schwarzian derivatives at symmetric points on the unit circle.     

Convolution properties of some classes of meromorphic univalent functions

Convolution technique and subordination theorem are used to study certain class of meromorphic univalent functions in the punctured unit disc.     

Generalizations of the area theorem for meromorphic univalent functions with nonzero pole

In this article, we consider meromorphic univalent functions f in the unit disc of the complex plane having a simple pole at z = α ∈ (0, 1) with nonzero residue b at z = α. In 1969, P.N. Chichra proved an area theorem for such functions. In this note, we generalize this theorem and prove an interesting consequence of this result.     

The Hadamard product of meromorphic univalent functions defined by using convolution

In this work the authors extend certain results concerning the Hadamard product for two classes related to starlike and convex univalent meromorphic functions with positive coefficients by using convolution.     

Extremal problems in classes of univalent functions,omitting prescribed values

Section 1 of the paper is devoted to extremal problems in the classes of conformal homeomorphisms of the circle and the annulus, connected directly with the problem on the maximum of the conformal modulus in the family of doubly connected domains. In Secs. 2 and 3 one considers the class R of functions f()=c₁+c₂²+... regular and univalent in the circleU={||<1} and such that f(₁)f(₂)=1 for ₁₂U (the class of Bieberbach-Eilenberg functions). Here one solves the problem of the maximum of |f(₀)| in the class of functions f()R with a fixed value f(₀, where ₀ is an arbitrary point U, and of the maximum of |f(₀)| in the entire class R. For the proof one makes use of the method of the moduli of families of curves.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova AN SSSR, Vol. 144, pp. 94–114, 1985.     

Forms for meromorphic functions

An infinite circular arithmetic is defined and used to define power sum and centered forms for meromorphic functions. The properties of these forms are investigated and it is shown that both the power sum and the centered forms form including chains with respect to their orders and that they possess a kind of quadratic convergence with respect to the domain circle. An example of the use of the forms is given.     

Extremal functions for sequences

Davenport-Schinzel sequences DS(s) are finite sequences of some symbols with no immediate repetition and with no alternating subsequence (i.e. of the type ababab …) of the length s. This concept based on a geometrical motivation is due to Davenport and Schinzel in the middle of 1960s. In the late 1980s strong lower and upper (superlinear) bounds on the maximum length of the DS(s) sequences on n symbols were found. DS(s) sequences are well known to computer geometrists because of their application to the estimates of the complexity of the lower envelopes.

Here we summarize some properties of the generalization of this concept and prove that the extremal functions of aa… abb… baa… abb… b grow linearly.     

Structure formulas for univalent functions

With the aid of special integrating factors for the Loewner-Kufarev equation, one determines the general form of the structure formulas for functions of the class S and one obtains a series of new concrete structure formulas for certain subclasses of functions from S.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova AN SSSR, Vol. 125, pp. 128–134, 1983.     

Covering theorems for univalent functions

Mathematische Zeitschrift -     

亚纯函数的唯一性定理

应用奈望里纳理论研究亚纯函数的唯一性问题,得到若干结果,推广了某些已知定理．