Definition:Branch Point

Definition
Let $U \subseteq \C$ be an open set.

Let $f : U \to \C$ be a complex multifunction.

A branch point of $f$ is a point $a$ in $U$ such that:


 * $f$ has more than one value at one or more points in every neighborhood of $a$
 * $f$ has exactly one value at $a$ itself.