Baernstein[2] gave the conclusion by using Koebe function as the extremal function , Glenn Schober[6] studied the classes such as S, P, K, S* of H(D) and represented these functions with integral formulations.

• Baernstein首先在单位圆上讨论给出了以Koebe函数作为极值函数的结论，Glenn Schober对H(D)中一些函数子类如S、P、K、S~*等作了研究，将这些子类上的函数用积分表达出来，王键结合Baernstein~*函数的定义及Glenn Schober的结论，定义了对称集的概念并得出了一些函数类在其上的积分平均。