= Reiter condition
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{title2=$\|\lambda(g)\mu_n-\mu_n\|_1\to0$}
= Reiter's condition
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{synonym}
For a countable discrete <group>, the <Reiter condition> requires a sequence of <probability measures> in $\ell^1(G)$ asymptotically invariant under every left translation. It is equivalent to the existence of an <invariant mean> and a <Følner sequence>. Separation by bounded functions shows that amenability gives approximate invariance simultaneously on each finite set of translations; countability makes the successive finite tests into a sequence.
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