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If $X_1$ and $X_2$ are reflexive Banach spaces and $p\in[1,\infty]$, then the product $X_1\times X_2$ with the norm $\|(u,v)\|=(\|u\|^p+\|v\|^p)^{\frac1p}$ is also a reflexive Banach space (all these norms are equivalent; the $\infty$-norm is simply the supremum of the values).

Now, let $(X_i)_{i\in I}$ be a collection of reflexives Banach spaces. Given a $p\in[1,\infty]$, one can define the corresponding Cartesian products $\bigoplus^p_IX_i$ as the set of all sequences in the product whose $p$-norm is finite:

$$\bigoplus^p_IX_i=\Big\{f\in \prod_IX_i\,\Big|\,\sum_I\|f(i)\|^p \text{ is finite}\Big\}$$ endowed with the $p$-norm. These are Banach spaces, but in general $\bigoplus^p_IX_i$ and $\bigoplus^q_IX_i$ are distinct (for $p=1$ this is the coproduct, and for $p=\infty$ the product).

Question

Is these spaces reflexive? Does the answer depend on $p$?

References would be appreciated.

PHL
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  • If yo'ure doing this kind of math, it's not a bad idea to work on your LaTeX skills. Notice the typographical difference between $|a||b|,$ coded as \|a\|\|b\|, and $||a|| ||b||,$ coded as ||a|| ||b||. That is the reason for my edit to this question. – Michael Hardy Mar 01 '22 at 21:15
  • See what happens when each $X_i=\Bbb R$. This might suggest an answer. – David Mitra Mar 01 '22 at 21:15
  • please see https://math.stackexchange.com/questions/872173/banach-valued-sequence-spaces-ellpx – Onur Oktay Mar 02 '22 at 15:16

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