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Jan 24, 2021 at 4:10 review Close votes
Feb 5, 2021 at 20:23
Jan 21, 2021 at 17:22 comment added Nate Eldredge In particular, see math.stackexchange.com/questions/209532/…. If $A \subset \mathbb{R}$ is a set with zero inner Lebesgue measure and nonzero outer Lebesgue measure, there is an extension $\mu'$ of Lebesgue measure to $\beta = \sigma(\mathcal{B} \cup \{A\})$ for which $\mu(A)=0$. But for any open set $U \supset A$ we have $\mu'(U) = m(U) \ge m^*(A) > 0$.
Jan 21, 2021 at 17:17 comment added Nate Eldredge I see, so you know only that it's inner and outer regular on Borel sets, but you want to know whether the outer regularity also holds on sets $A \in \beta$ which are not necessarily Borel. I don't think it is true.
Jan 21, 2021 at 17:10 history edited evaristegd CC BY-SA 4.0
Add link to post about regular measures
Jan 21, 2021 at 17:08 comment added evaristegd @NateEldredge , thanks for the comment. Regarding the level of the question, I thought it was of a level high enough for MO; however, I'll be more cautious and try MathSE instead next time. Re: regularity, similarly to this post, I define regularity as having both inner regularity and outer regularity.
Jan 21, 2021 at 17:01 comment added Nate Eldredge I'm not sure whether this is a research-level question; Math.SE might be more suitable. But either way, can you state precisely what you mean by "$\mu$ is regular"? Different authors use different definitions, and for some, the statement you want to prove is literally part of the definition of being regular.
Jan 21, 2021 at 16:32 review First posts
Jan 21, 2021 at 16:36
Jan 21, 2021 at 16:30 history asked evaristegd CC BY-SA 4.0