1Fang M.L,Chang J.M. Normal families and multiple values[J].Archiv der Mathematik,2007.560-568.doi:10.1111/j.1528-1167.2010.02669.x.
2Xia J.Y,Xu Y. Normal families of meromorphic functions with multiple values[J].Journal of Mathematical Analysis and Applications,2009.387-393.doi:10.1016/j.jmaa.2009.01.003.