Hadamard products and QK spaces

Let f (z) = ∞n=0 anzn and g(z) = ∞n=0 bnzn be analytic in the unit disk. The Hadamard product of f and g is defined by f ∗ g(z) = ∞n=0 anbnzn. This paper gives some characterizations of functions in QK spaces in terms of the Hadamard products. © 2007 Elsevier Inc. All rights reserved.