= Layer-cake extraction of Følner sets
For a finitely supported nonnegative function $\mu$ of sum one, let $F_t=\{x:\mu(x)>t\}$. Then $\int_0^\infty|F_t|\,dt=1$ and $\int_0^\infty|F_t\mathbin\triangle gF_t|\,dt=\|\mu-\lambda(g)\mu\|_1$. If the sum of these latter integrals over a finite set of translations is less than $\varepsilon$, some nonempty level set has the sum of its relative boundaries less than $\varepsilon$. This converts the <Reiter condition> into finite <Følner sets> without assuming that the <group> is finitely generated.
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