Normal Criteria of Function Families Concerning Shared Values

Abstract

We study the normality of families of meromorphic functions concerning shared values. We consider whether a family of meromorphic functions F is normal in $D$, if, for every pair of functions $f$ and $g$ in F, $f^{\prime }-a{f}^{-n}$ and $g^{\prime }-a{g}^{-n}$ share the value b, where a and b are two finite complex numbers such that $a\ne 0$, n is a positive integer. Some examples show that the conditions in our results are best possible.