Koebe quarter theorem
(重定向自Koebe function)
In complex analysis, a branch of mathematics, the Koebe 1/4 theorem states the following:
The theorem is named after Paul Koebe, who conjectured the result in 1907. The theorem was proven by Ludwig Bieberbach in 1916. The example of the Koebe function shows that the constant 1/4 in the theorem cannot be improved.