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Banach spaces, function spaces, real functions, integral transforms, theory of distributions, measure theory.

7 votes
0 answers
473 views

Characterizing the sum $L^1 + L^\infty + L^{1,\infty} + L^{\infty, 1}$ of iterated Lebesgue ...

For the usual Lebesgue spaces $L^p (\mu)$ ($p \in [1,\infty]$) on a ($\sigma$-finite) measure space $(X,\mu)$, it is well-known that one has the characterization $$ L^p (\mu) = \left\{f : X \to \Bbb{ …
PhoemueX's user avatar
  • 734
5 votes
1 answer
374 views

Sufficient criteria for $X \subset \mathcal{H}$ to be a Lipschitz (or unif. cont.) retract o...

I am interested in sufficient criteria which ensure that a subset $X$ of a Hilbert space $\mathcal{H}$ is a Lipschitz (or at least uniformly continuous) retract of $\mathcal{H}$. Under which condi …
PhoemueX's user avatar
  • 734
1 vote
Accepted

Insights about a frame-like inequality

Yes, your starting inequality can only hold if $H$ has finite dimensional range. In fact, the dimension can be at most $q$. To see this, let $Y$ denote the range of $H$. Your inequality implies (why? …
PhoemueX's user avatar
  • 734