Let $F(x)$ be a real-analytic function near $0$ ,with $0$ as one of its fixpoints and $f ' (0) > 1$.
$$F(x) = F \circ F \circ F^{-1} = \lim_{n \to \infty} F^{n} \circ F \circ F^{-n} = \lim_{n \to \infty} F^{n}(f'(0)\cdot F^{-n}(x)) $$
($*^n$ is $n$th composition)
How to prove this ?
Where does this expression $\lim_{n \to \infty} F^{n}(f'(0)\cdot F^{-n}(x)) $ converge ? I assume the radius of convergeance of $F^{-1}(x)$ places an upper boundary on where this can converge. But I assume this is also true for the radius of convergeance of $F(x)$. I assume this expression converges exactly in a circle centered at $0$ with radius $T$. Where $T$ is the smallest of the ROC of both $F(x)$ and $F^{-1}(x)$.
( I assume convergeance implies convergeance to the correct value ? )
I understand $f'(0) x$ is a good approximation for $F(x)$ near $0$ and that $F^{-n}(x)$ goes to $0$ but Im not convinced. I want proofs.
I assume l'Hopital can not be used here ??
Hint received from tommy1729 :
Plug in the koenigs function.
Brilliant !