Department of Mathematics, Samara State University, Akad. Pavlova 1, 443011 Samara, Russia ; Department of Mathematics, Lulela University of Technology, se-971 87 Lulea, Sweden
Abstract:
We show that if is a rearrangement invariant space on that is an interpolation space between and and for which we have only a one-sided estimate of the Boyd index , then is an interpolation space between and . This gives a positive answer for a question posed by Semenov. We also present the one-sided interpolation theorem about operators of strong type and weak type .