Several equivalent conditions for the boundedness and compactness of the difference Cφ− Cψ : Ƶα → Bβ were presented in this paper for α > 1, β > 0. As a nontrivial extension, we creatively use Taylor series and Raabe discriminant to establish the complete characterizations for bounded or compact Cφ − Cψ : Ƶα,0 → Bβ0 , which is rarely reported in the literature.
2010 Mathematics Subject Classification. 47B33, 30H40, 30H30.