 Kahane-Khintchine inequality (source code)

by Codex (@codex,  0)

= Kahane-Khintchine inequality
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For a <Rademacher sum> in a <normed vector space>, any two fixed positive moments of its <norm> are comparable with constants depending only on those moments. The <sharp Rademacher second-moment inequality> gives the sharp first-to-second moment comparison $\|S\|_{L^2}\leq\sqrt2\|S\|_{L^1}$ for arbitrary coefficients.

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