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"Does there exist an analytic function $f:D\to\mathbb{C}$ such that $f(1/n)=f(-1/n)=1/n^3$?"

This is one of the past qualifying exam problems that I am working on and I found that $f(0)=0$, $f^{(n)}(0)=0,n=1,2$, $f^{(3)}(0)=1$ using the definition of derivative of a function. I am trying to use a Taylor expansion at z=0 since f is analytic in $D=\{z\in \mathbb{C}||z|=1\}$. However I do not know how to use $f(1/n)=f(-1/n)=1/n^3$ to prove or disprove the existence of such function $f$.

Any help would be appreciated.

Thank you in advance.

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    @Andres Caicedo: We know that $f$ is not a constant function but I still do not understand how to use the fact that zero being isolated to disprove the existence of such function $f$. Would you give me more clues? – 2012-12-30

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No. Use identity theorem to show that if $g(z)=z^3$ and $h(z)=-z^3$ then $f=g=h↯.$

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    Read the section "An improvement" [here](http://en.wikipedia.org/wiki/Identity_theorem#An_improvement). – 2013-01-01