arXiv subjects

Estelle Basset

Publications and source records attributed to Estelle Basset.

3 recordsLinked to original sources

arXiv2026

On metric characterizations of tree and fragmentability indices of Banach spaces

We introduce two ordinal indices that are linear invariants for Banach spaces: the dyadic tree index and the sprawling tree index. We show that they are also bi-Lipschitz invariants. In fact, we characterize their values in terms of sub-Lipschitz embeddability of dyadic or countably branching diamond graphs of ordinal height. We derive applications for separable Banach spaces that are universal for complete countable metric spaces and bi-Lipschitz embeddings. We also discuss the links of these tree indices with classical fragmentability indices of Banach spaces such as the dentabilty, weak fragmentability and Szlenk indices.

math.FA↗

arXiv2025

Diversity of Lipschitz-free spaces over countable complete discrete metric spaces

We show that there are uncountably many mutually non-isomorphic Lipschitz-free spaces over countable, complete, discrete metric spaces. Also there is a countable, complete, discrete metric space whose free space does not embed into the free space of any uniformly discrete metric space. This enhanced diversity is a consequence of the fact that the dentability index $D$ presents a highly non-binary behavior when assigned to the free spaces of metric spaces outside of the oppressive confines of compact purely 1-unrectifiable spaces. Indeed, the cardinality of $\{D(\mathcal F(M)): M$ countable, complete, discrete$\}$ is uncountable while $\{D(\mathcal F(M)):M$ infinite, compact, purely 1-unrectifiable$\}=\{ω,ω^2\}$. Similar barrier is observed for uniformly discrete metric spaces as higher values of the dentability index are excluded for their free spaces: $\{D(\mathcal F(M)):M$ infinite, uniformly discrete$\}=\{ω^2,ω^3\}$.

math.FA↗

arXiv2025

On the weak-fragmentability index of some Lipschitz-free spaces

We show the existence of Lipschitz-free spaces verifying the Point of Continuity Property with arbitrarily high weak-fragmentability index. For this purpose, we use a generalized construction of the countably branching diamond graphs. As a consequence, we deduce that to be Lipschitz-universal for countable complete metric spaces, a separable complete metric space cannot be purely 1-unrectifiable. Another corollary is the existence of an uncountable family of pairwise non-isomorphic Lipschitz-free spaces over purely 1-unrectifiable metric spaces. Some results on compact reduction are also obtained.

math.FA↗