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Inspired by Pitt's theorem and this post we ask the following question:

First we remind the Pitt's theorem and also introduce a particular Banach space as averaging of $\ell^p$ spaces for $1\leq p \leq 2$

Pitt's theorem: Every bounded operator $T:\ell^q \to \ell^p$, $p<q$ is a compact operator.

Now consider $X=\ell_1$ with new norm $|x|=\int_1^2 |x|_pdp$ the completion of this normed space is denoted by $\tilde{X}$.

Question: Assume that $T:\tilde{X}\to \ell^1$ is a bounded operator. Is $T$ necessarilly a compact operator?

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  • $\begingroup$ How would this be a generalization (rather than an "adaptation") of Pitt's theorem? $\endgroup$ Commented Apr 6, 2023 at 13:27
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    $\begingroup$ If the space contains a complemented subspace isomorphic to $l^1$ then clearly the answer is no. $\endgroup$
    – S Argyros
    Commented Apr 6, 2023 at 15:15

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