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I am trying to understand the proof that the family of analytic functions with positive real part is normal from here.

One considers the Mobius transformation $T(z)=\frac{1+z}{1-z}$ that maps the right half plane $G$ to the unit disk $D$. Then the family $F'=\{\frac{1+f}{1-f}\,| \, f \in F \}$ being locally bounded is normal.

Thus we get for $g_n \in F' \,\, \exists g_{n_k} \to g $ uniformally on compact subsets of $D$.

How does one show that for $T^{-1}(z)=\frac{z-1}{z+1}$, this implies $T^{-1}(g_{n_k})=f_{n_k} \to f=T^{-1}(g)$ on compact subsets of $G$? Is this true in general or do we need some bound like for all $f \in F$, we have $|f(a)| \leq M$ for some point $a \in G$ where $M >0$.

RobPratt
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    The fact that is needed is that the derivative $\frac d{dz}T^{-1}(z)$ is bounded on compact subsets. That can control the distance from $T^{-1}(g_m(z))$ to $T^{-1}(g(z))$ in terms of the distance from $g_m(z)$ to $g(z)$ via the mean value theorem. – Greg Martin Aug 28 '22 at 23:41

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