Koebe quarter theorem
= Koebe quarter theorem
{c}
{wiki}
= Koebe one-quarter theorem
{c}
{synonym}
If $f$ is a <univalent function> on the <unit disc>, then $B(f(0),|f'(0)|/4)\subseteq f(\mathbb D)$. The constant $1/4$ is sharp, as shown by the <Koebe function>. This gives useful comparisons between the <derivative> of a <conformal map>, its <conformal radius>, and its distance to the <domain boundary>.