- Let \(f ( z ) \in H ( \mathbb { D } ) , \operatorname { R e } ( f ( z ) ) > 0 , f ( 0 ) = a > 0\) . Show that
\[ | \frac { f ( z ) - a } { f ( z ) + a } | \leq | z | , | f ^ { \prime } ( 0 ) | \leq 2 a . \]
- Show that the above is still true if \(\mathrm { R e } ( f ( z ) ) > 0\) is replaced with \(\mathrm { R e } ( f ( z ) ) \geq 0\)