We develop sufficient conditions for various types of starlikeness for functions analytic in the unit disk. The problems that we consider are more general than similar problems considered by previous authors. Furthermore we obtain stronger estimates than in earlier works and in several cases sharp ones.

In this article some problems related to the Krzyż conjecture are discussed. In particular, we prove the Krzyż conjecture for the fifth coefficient.

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AbstractWe develop sharp conditions for various types of starlikeness for functions analytic in the unit disk with bounded derivatives. We also describe the precise range {zf′(z)/f(z): z ∈ D, f ∈ }, where f ∈ means f (0) = 0, f′(0) = 1, and |f′(z) - 1 |< ≦ λ in the unit disc D, and draw some cnoslusions from that.