# Holomorphic functions (全纯)

Definition 1 Let $\Omega$ be an open set in $\mathbb C$ and $f$ a complex-valued function on $\Omega$. The function $f$ is holomorphic at the point $z_0\in \Omega$ if the quotient

$$\dfrac{f(z_0+h)-f (z_0)}{h}$$