  In this note, we show some improvements for Theorem 7 and Example 8 in
Shiping Wang[Information Sciences 263(1), 186-197, 2014]. Concretely, we study
further the sixth lower and upper approximations of sets for covering
approximation spaces. Furthermore, we present the sixth dual lower and upper
approximations of sets for covering approximation spaces. We also construct the
sixth dual lower and upper approximations of sets from the view of matrix.
Throughout, we use the same notations as Shiping Wang[Information Sciences
263(1), 186-197, 2014].
