© 2004 by Oxford University Press
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A useful estimate for the decreasing rearrangement of the sum of functions
1 Departament de Matemàtica Aplicada i Anàlisi, Universitat de Barcelona, E-08071 Barcelona, Spain
Given f=
n
N fn, where {fn}n are measurable functions, we show that f*(3t)
n ( fn*(t) +1/t
cnttfn*(s) ds ), where {cn}n
N are positive numbers such that
n cn=1. Several consequences in the setting of weighted Lorentz spaces are also given.
Received 12 October 2001.