ESTIMATES OF THE SECOND DERIVATIVE OF BOUNDED ANALYTIC FUNCTIONS

Assume a point $z$ lies in the open unit disk $\mathbb{D}$ of the complex plane $\mathbb{C}$ and $f$ is an analytic self-map of $\mathbb{D}$ fixing 0. Then Schwarz’s lemma gives $|f(z)|\leq |z|$, and Dieudonné’s lemma asserts that $|f^{\prime }(z)|\leq \min \{1,(1+|z|^{2})/(4|z|(1-|z|^{2}))\}$. We prove a sharp upper bound for $|f^{\prime \prime }(z)|$ depending only on $|z|$.

A Geometric Extension of Schwarz’s Lemma and Applications

Let f be a holomorphic function of the unit disc , preserving the origin. According to Schwarz’s Lemma, |f'(0)| ≤ 1, provided that . We prove that this bound still holds, assuming only that f() does not contain any closed rectilinear segment [0, eiϕ], ϕ ∊ [0, zπ], i.e., does not contain any entire radius of the closed unit disc. Furthermore, we apply this result to the hyperbolic density and give a covering theorem.