Identity theorem for Riemann surfaces

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In mathematics, the identity theorem for Riemann surfaces is a theorem that states that a holomorphic function is completely determined by its values on any subset of its domain that has a limit point.

[edit] Statement of the theorem

Let $X$ and $Y$ be Riemann surfaces, and let $f : X \to Y$ be holomorphic. Suppose that $f | A = g | A$ for some subset $A \subseteq X$ that has a limit point, where $f|_{A} : A \to Y$ denotes the restriction of $f$ to $A$ . Then $f = g$ (on the whole of $X$ ).