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Condor5
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Fatou's lemma and dominated convergence for nets and the counting measure

I'm wondering if anyone has shown Fatou's lemma for sums when the limits are taken over nets.

That is, has anyone proved the following?

If $\{x_{k,\alpha}\}_{k\in \mathbb N,\alpha \in \mathcal A}$ with $\mathcal A$ a directed set, then

$$\sum_{k=1}^{\infty} \sup_{\bar \alpha}\inf_{\alpha\geq \bar \alpha} x_{k,\alpha}\leq \sup_{\bar \alpha}\inf_{\alpha\geq \bar \alpha} \sum_{k=1}^{\infty} x_{k,\alpha}.$$

This result is not true if the sum were replaced by a general measure.

Condor5
  • 165
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