Proposition If y(t), b(t) ∈ VDF ∩ VH(μ) ([1]), then||Ky||μ≤q||b||μ||y||μ,(1)where q is a constant and Ky=-b(t)/πi L0 y(s) (ζ(t))ds.Proof. Let w(t) =1/πi L0 y(s)- y(t)/s-t ds and t1-t0=h. Suppose a path l = t’t0 U t0t″, we obtainBy a complicated calculation, it can be got