Normal Criteria of Function Families Concerning Shared Values

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′−af−n and g′−ag−n share the value b, where a and b are two finite complex numbers such that a≠0, n is a positive integer. Some examples show that the conditions in our results are best possible