Theorem [1] Suppose $\Omega$ is an open convex set in $\mathbb{C}$, suppose $f$ is a holomorphic function $f:\Omega\to\mathbb{C}$, and suppose $a,b$ are distinct points in $\Omega$. Then there exist points $u,v$ on $L_{{ab}}$ (the straight line connecting $a$ and $b$ not containing the endpoints), such that

where $\Re$ and $\Im$ are the real and imaginary parts of a complex number, respectively.