Differential subordinations and inequalities in the complex plane
Let f and F be analytic in the unit disc U. The function f is subordinate to F, written \(f\prec F\) or f(z)\(\prec F(z)\), if F is univalent, \(f(0)=F(0)\) and f(U)\(\subset F(U)\). The authors deal with second order differential subordinations of the form \((1)\quad \psi (p(z),zp'(z),z^ 2p''(z);z)\prec h(z),\) where \(\psi\) : \({\mathbb{C}}^ 3\times U\to {\mathbb{C}}\). They generalize their previous results [see, Mich. Math. J. 28, 157-171 (1981; Zbl 0439.30015)] on the case (1). With help from this generalization they prove some new inequalities, for example: Theorem 6. If p is analytic in U with \(p(0)=0\), then \(| zp'(z)| +z^ 2p''(z)/p(z)| <1\) implies that \(| p(z)| <1;\) Theorem 7. If p is analytic in U with \(p(0)=1\), and if \(Re[2p(z)- zp''(z)/p'(z)-1]>0,\) then Re p(z)\(>0\).
second order differential subordinations
scientific article; zbMATH DE number 4029976