Factorizing the Classical Inequalities

Grahame Bennett

1996년 1월 · American Mathematical Society: Memoirs of the American Mathematical Society 576권 · American Mathematical Soc.

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This volume describes a new way of looking at the classical inequalities. The most famous such results (Hilbert, Hardy, and Copson) may be interpreted as inclusion relationships, $l^p\subseteq Y$, between certain (Banach) sequence spaces, the norm of the injection being the best constant of the particular inequality. The authors' approach is to replace $l^p$ by a larger space, $X$, with the properties: $\Vert l^p\subseteq X\Vert =1$ and $\Vert X\subseteq Y\Vert =\Vert l^p\subseteq Y\Vert$, the norm on $X$ being so designed that the former property is intuitive. Any such result constitutes an enhancement of the original inequality, because you now have the classical estimate, $\Vert l^p\subseteq Y\Vert$, holding for a larger collection, $X=Y$. The authors' analysis has some noteworthy features: The inequalities of Hilbert, Hardy, and Copson (and others) all share the same space $Y$. That space-alias ces($p$ )-being central to so many celebrated inequalities, the authors conclude, must surely be important. It is studied here in considerable detail. The renorming of $Y$ is based upon a simple factorization, $Y= l^p\cdot Z$ (coordinatewise products), wherein $Z$ is described explicitly. That there is indeed a renorming, however, is not so simple. It is proved only after much preparation when duality theory is considered.