Using the Baire Category Theorem to Explore Lions Problem for Quasi-Banach Spaces
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| Format: | Preprint |
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2024
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| _version_ | 1866914992720183296 |
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| author | Aksoy, A. G. Almira, J. M. |
| author_facet | Aksoy, A. G. Almira, J. M. |
| contents | Many results for Banach spaces also hold for quasi-Banach spaces. One important such example is results depending on the Baire Category Theorem (BCT). We use the BCT to explore Lions problem for a quasi-Banach couple $(A_0, A_1)$. Lions problem, posed in 1960's, is to prove that different parameters $(θ,p)$ produce different interpolation spaces $(A_0, A_1)_{θ, p}$. We first establish conditions on $A_0$ and $A_1$ so that interpolation spaces of this couple are strictly intermediate spaces between $A_0+A_1$ and $A_0\cap A_1$. This result, together with a reiteration theorem, gives a partial solution to Lions problem for quasi-Banach couples. We then apply our interpolation result to (partially) answer a question posed by Pietsch. More precisely, we show that if $p\neq p^*$ the operator ideals $\mathcal{L}^{(a)}_{p,q}(X,Y)$, $\mathcal{L}^{(a)}_{p^*,q^*}(X,Y)$ generated by approximation numbers are distinct. Moreover, for any fixed $p$, either all operator ideals $\mathcal{L}^{(a)}_{p,q}(X,Y)$ collapse into a unique space or they are pairwise distinct. We cite counterexamples which show that using interpolation spaces is not appropriate to solve Pietsch's problem for operator ideals based on general $s$-numbers. However, the BCT can be used to prove a lethargy result for arbitrary $s$-numbers which guarantees that, under very minimal conditions on $X,Y$, the space $\mathcal{L}^{(s)}_{p,q}(X,Y)$ is strictly embedded into $\mathcal{L}^{\mathcal{A}}(X,Y)$. The paper is dedicated to the memory of Prof. A. Pietsch, who passed away recently. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2408_14893 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | Using the Baire Category Theorem to Explore Lions Problem for Quasi-Banach Spaces Aksoy, A. G. Almira, J. M. Functional Analysis Classical Analysis and ODEs Many results for Banach spaces also hold for quasi-Banach spaces. One important such example is results depending on the Baire Category Theorem (BCT). We use the BCT to explore Lions problem for a quasi-Banach couple $(A_0, A_1)$. Lions problem, posed in 1960's, is to prove that different parameters $(θ,p)$ produce different interpolation spaces $(A_0, A_1)_{θ, p}$. We first establish conditions on $A_0$ and $A_1$ so that interpolation spaces of this couple are strictly intermediate spaces between $A_0+A_1$ and $A_0\cap A_1$. This result, together with a reiteration theorem, gives a partial solution to Lions problem for quasi-Banach couples. We then apply our interpolation result to (partially) answer a question posed by Pietsch. More precisely, we show that if $p\neq p^*$ the operator ideals $\mathcal{L}^{(a)}_{p,q}(X,Y)$, $\mathcal{L}^{(a)}_{p^*,q^*}(X,Y)$ generated by approximation numbers are distinct. Moreover, for any fixed $p$, either all operator ideals $\mathcal{L}^{(a)}_{p,q}(X,Y)$ collapse into a unique space or they are pairwise distinct. We cite counterexamples which show that using interpolation spaces is not appropriate to solve Pietsch's problem for operator ideals based on general $s$-numbers. However, the BCT can be used to prove a lethargy result for arbitrary $s$-numbers which guarantees that, under very minimal conditions on $X,Y$, the space $\mathcal{L}^{(s)}_{p,q}(X,Y)$ is strictly embedded into $\mathcal{L}^{\mathcal{A}}(X,Y)$. The paper is dedicated to the memory of Prof. A. Pietsch, who passed away recently. |
| title | Using the Baire Category Theorem to Explore Lions Problem for Quasi-Banach Spaces |
| topic | Functional Analysis Classical Analysis and ODEs |
| url | https://arxiv.org/abs/2408.14893 |