152  L07 : Proof of Lemmas 4-6 for the outer-measure extension construction

Measure Theoretic Probability - Jem Corcoran

Published

April 17, 2026

Keywords

measure theory, probability, sigma algebra, outer measure, lemmas

Video 152.1: Lesson 7: Proof of Lemmas 4–6 for the outer-measure extension construction.

152.1 Lesson map

This lesson proves the next three lemmas from the extension roadmap.

  • Recap: extending P from a field \mathcal{F}_0 to \mathcal{F}=\sigma(\mathcal{F}_0).
  • Recall the outer measure P^*.
  • Important warning: do not use that P^* is a probability measure yet.
  • Recall the definition of \mathcal{M}.
  • Lemma 4:
  • Lemma 5:
  • Lemma 6:

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Figure 152.14