文摘
We consider the general Hardy type operator brary/content/render" xmlns="http://www.w3.org/1998/Math/MathML">b>Hkb>f(x)=bsup>∫0xbsup>k(x,t)f(t)dt, where brary/content/render" xmlns="http://www.w3.org/1998/Math/MathML">k(x,t) is a positive and measurable kernel. To characterize the weights u and v so that brary/content/render" xmlns="http://www.w3.org/1998/Math/MathML">b>Hkb>:b>Lpb>(u)→b>Lqb>(v) is still an open problem for any parameters p and q. However, for special cases the solution is known for some parameters p and q. In this paper the current status of this problem is described and discussed mainly for the case brary/content/render" xmlns="http://www.w3.org/1998/Math/MathML">1<p≤q<∞. In particular, some new scales of characterizations in classical situations are described, some new proofs and results are given and open questions are raised.