In this manuscript, we examine the continuity properties of the Riemann-Liouville fractional integral for order α=1/p, where p>1, mapping from Lp(t0,t1;X) to the Banach space BMO(t0,t1;X)∩K(p−1)/p(t0,t1;X). This improvement, refines a result by Hardy-Littlewood. To achieve this, we study properties between spaces BMO(t0,t1;X) and K(p−1)/p(t0,t1;X). Additionally, we obtained the boundedness of the fractional integral of order α≥1 from L1(t0,t1;X) into the Riemann-Liouville fractional Sobolev space WRLs,p(t0,t1;X).
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