E. Harboure et al., BOUNDEDNESS OF THE FRACTIONAL INTEGRAL ON WEIGHTED LEBESGUE AND LIPSCHITZ-SPACES, Transactions of the American Mathematical Society, 349(1), 1997, pp. 235-255
Necessary and sufficient conditions are given for the fractional integ
ral operator I-alpha to be bounded from weighted strong and weak L(p)
spaces within the range p greater than or equal to n/alpha into suitab
le weighted BMO and Lipschitz spaces. We also characterize the weights
for which I-alpha can be extended to a bounded operator from weighted
BMO into a weighted Lipschitz space of order alpha. Finally, under an
additional assumption on the weight, we obtain necessary and sufficie
nt conditions for the boundedness of I-alpha between weighted Lipschit
z spaces.