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Large scale properties of groups; growth functions; Dehn functions; small cancellation properties; hyperbolicity and CAT(0); actions and representations; combinatorial group theory; presentations

4 votes
1 answer
506 views

Amenable subsets of groups

Let $X$ be a subset of a group $G$. We say that $X$ is left amenable with respect to $G$ if there is a function $\mu:\mathcal P(G)\to [0,\infty]$ with the following three properties. $\mu(A\cup B)=\m …
Karl Lorensen's user avatar
4 votes
Accepted

Amenable subsets of groups

Here is a slightly modified version of an example that was communicated to the author of the question by Nicolas Monod. Let $k>1$ be an integer and $G$ the Baumslag-Solitar group $\mathrm{BS}(1,k)$; t …
Karl Lorensen's user avatar