
Let \({\mathbf S}\) denote the usual class of normalized, univalent functions \(f(z)=z+a_2z^2+\dots\) in the unit disk. It is known that for \(f\in {\mathbf S}\), the inequality \(0\leq\alpha (f):= \lim_{n\to\infty} |a_n|/n \leq 1\) holds. Set \(\sigma_n(f): =(a_2,\dots,a_n)\). The \(n\)th coefficient region \(V_n\subset C^{n-1}\) is the set \(V_n:=\{\sigma_n(f): f\in{\mathbf S}\}\). Suppose that \(a\in\text{int} V_N\), that the sequence \(\{\varepsilon_n\}\) of positive numbers \(\varepsilon_n\) has limit zero, and that an infinite set \(E\) of disjoint intervals of integers is given. The authors prove that there exists a function \(f\in S\) with the following properties: (i) \(\sigma_N(f)=a\); (ii) \(a_n=0(n\in I)\) for infinitely many intervals \(I\) in \(E\); and (iii) \(|a_n|>n \varepsilon_n (n\in I)\) for infinitely many intervals \(I\) in \(E\). If the coefficients \(a_n\) are real, then the inequality in (iii) can be strengthened to \(a_n>n\varepsilon_n\) \((n\in I)\). The authors do not know whether there is a function \(f\in{\mathbf S}\) with properties (i), (ii), and (iii) all of whose coefficients are nonnegative. For the prescribed initial \(N\) coefficients, the sequence \(\{\varepsilon_n\}\), and the set \(E\) of intervals of integers, the authors inductively construct the function \(f\in S\) from polynomials.
coefficient region, General theory of univalent and multivalent functions of one complex variable, functions in the unit disk, Chebyshev polynomial, Power series (including lacunary series) in one complex variable
coefficient region, General theory of univalent and multivalent functions of one complex variable, functions in the unit disk, Chebyshev polynomial, Power series (including lacunary series) in one complex variable
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