Some Inequalities of differential polynomials II
  In this paper, we consider the value distribution of the differential polynomials $f^2f^{(k)}-1$ where $k$ is a positive integer, and obtain some estimates only by the reduced counting function. Our result answers a question in (Some inequalities of differential polynomials, Mathematical Inequalities and Applications, \textbf{12}(2009), no.1, 99--113) completely. 
Junfeng Xu, Hongxun Yi and Zhanliang Zhang
math.CV