If I have a question which has been posted here in MSE before, and if, after following the hints give by someone there I still got stuck, can I post the problem again without getting branded as "duplicate"? Specifically, here is what I would like to post:


I have been working on the same problem posted in 2013 here. I followed closely the hints given by @martini there, but nevertheless I still got stuck. Here are what I have gone so far:

(1) Let $F_n = \{\{1\}, \{2\}, \ldots \{n\}\}$, let $\sigma(F_n)$ be its $\sigma$-algebra, and let make this example simple by making $n=2$ only
(2) If $F_1:=\{1\}$, then $\sigma(F_1)=\{\emptyset,\{1\},\{1\}^c,\mathbb N \}$
(3) If $F_2:=\{\{1\},\{2\}\}$, then $\sigma(F_2)=\{\emptyset,\{1\},\{1\}^c,\{2\},\{2\}^c \{1,2\},\{1,2\}^c,\mathbb N\}$
(4) Here $\sigma(F_1) \cup \sigma(F_2)=\sigma(F_2)$, and $\sigma(F_2)$ is a $\sigma$-algebra. Therefore it looks like my example fails.

What did I do wrong with my analysis? Thank you for your time and help.


Please let me know, I don't want to break the community rule. Thank you.

  • 5
    $\begingroup$ Your new question looks quite different from the old one and importantly, it links to the old one so there's little chance of duplicate effort or that anyone will suspect poor intent. You might want to restate the problem, rather than just having it in the link (you could just copy and paste), but I think you'd probably be fine posting this. $\endgroup$ – Milo Brandt Jan 29 '15 at 4:43
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    $\begingroup$ I am 1000% sure that this question (here on meta) is a duplicate. $\endgroup$ – Asaf Karagila Jan 29 '15 at 5:29
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    $\begingroup$ Related older question: Clarify an old answer $\endgroup$ – Martin Sleziak Jan 29 '15 at 6:39
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    $\begingroup$ Thanks to all of you! $\endgroup$ – Amanda.M Jan 29 '15 at 13:25
  • $\begingroup$ @Meelo : I posted the question and got a very fruitful responses! Thanks guys!(I posted here: math.stackexchange.com/questions/1124929/… ) $\endgroup$ – Amanda.M Jan 29 '15 at 17:14
  • $\begingroup$ My answer at this question basically answers this. Does anyone have a better duplicate meta question? $\endgroup$ – 6005 Feb 8 '15 at 22:54

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