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ABSTRACT The first named author introduced the notion of upper stability for metric spaces in F. Baudier, Barycentric gluing and geometry of stable metrics, Rev. R. Acad. Cienc. Exactas Fís. Nat. Ser. A Mat. RACSAM  116 no. 1, (2022), 48 as a relaxation of stability. The motivation was a search for a new invariant to distinguish the class of reflexive Banach spaces from stable metric spaces in the coarse and uniform category. In this paper we show that property Q does in fact imply upper stability. We also provide a direct proof of the fact that reflexive spaces are upper stable by relating the latter notion to the asymptotic structure of Banach spaces. 

By discretizing an argument of Kislyakov, Naor and Schechtman proved that the 1-Wasserstein metric over the planar grid $\{0,1,\dots <\#comment/>,n{\}}^2$has $L_1$-distortion bounded below by a constant multiple of $\sqrt{\log <\#comment/>n}$. We provide a new “dimensionality” interpretation of Kislyakov’s argument, showing that if $\{G_n{\}}_{n=1}^{\mathrm{\infty <\#comment/>}}$is a sequence of graphs whose isoperimetric dimension and Lipschitz-spectral dimension equal a common number $\mathrm{\delta <\#comment/>}\in <\#comment/>[2,\mathrm{\infty <\#comment/>})$, then the 1-Wasserstein metric over $G_n$has $L_1$-distortion bounded below by a constant multiple of $(\log <\#comment/>|G_n|{)}^{\frac{1}{\mathrm{\delta <\#comment/>}}}$. We proceed to compute these dimensions for $\oslash <\#comment/>$-powers of certain graphs. In particular, we get that the sequence of diamond graphs $\{{\mathsf{D}}_n{\}}_{n=1}^{\mathrm{\infty <\#comment/>}}$has isoperimetric dimension and Lipschitz-spectral dimension equal to 2, obtaining as a corollary that the 1-Wasserstein metric over ${\mathsf{D}}_n$has $L_1$-distortion bounded below by a constant multiple of $\sqrt{\log <\#comment/>|{\mathsf{D}}_n|}$. This answers a question of Dilworth, Kutzarova, and Ostrovskii and exhibits only the third sequence of $L_1$-embeddable graphs whose sequence of 1-Wasserstein metrics is not $L_1$-embeddable. 

In this article we start a systematic study of the bi-Lipschitz geometry of lamplighter graphs. We prove that lamplighter graphs over trees bi-Lipschitzly embed into Hamming cubes with distortion at most 6. It follows that lamplighter graphs over countable trees bi-Lipschitzly embed into l1. We study the metric behaviour of the operation of taking the lamplighter graph over the vertex-coalescence of two graphs. Based on this analysis, we provide metric characterisations of superreflexivity in terms of lamplighter graphs over star graphs or rose graphs. Finally, we show that the presence of a clique in a graph implies the presence of a Hamming cube in the lamplighter graph over it. An application is a characterisation, in terms of a sequence of graphs with uniformly bounded degree, of the notion of trivial Bourgain–Milman–Wolfson type for arbitrary metric spaces, similar to Ostrovskii’s characterisation previously obtained in Ostrovskii (C. R. Acad. Bulgare Sci. 64(6), 775–784 (2011)). 

We prove that the class of reflexive asymptotic-$$c_{0}$$ Banach spaces is coarsely rigid, meaning that if a Banach space $$X$$ coarsely embeds into a reflexive asymptotic-$$c_{0}$$ space $$Y$$, then $$X$$ is also reflexive and asymptotic-$$c_{0}$$. In order to achieve this result, we provide a purely metric characterization of this class of Banach spaces. This metric characterization takes the form of a concentration inequality for Lipschitz maps on the Hamming graphs, which is rigid under coarse embeddings. Using an example of a quasi-reflexive asymptotic-$$c_{0}$$ space, we show that this concentration inequality is not equivalent to the non-equi-coarse embeddability of the Hamming graphs.