Notation Question: What Does \bigcup^{N}_{1}x_{n} Mean?

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Discussion Overview

The discussion revolves around the notation \bigcup^{N}_{1}x_{n} and its interpretation within the context of set theory. Participants explore the implications of the notation, particularly regarding finite, countable, and uncountable unions of sets.

Discussion Character

  • Technical explanation, Conceptual clarification, Debate/contested

Main Points Raised

  • One participant suggests that \bigcup^{N}_{1}x_{n} represents the union of sets x_{1}, x_{2}, ..., x_{N}.
  • Another participant counters that N could be infinite, indicating that the union could extend indefinitely, represented as x_{1} ∪ x_{2} ∪ x_{3} ∪ ...
  • A further point is raised regarding the possibility of N being uncountable, which complicates the listing of sets and suggests that such an interpretation could be misleading.
  • A participant expresses concern about the notation being used without prior explanation in a theorem, highlighting the importance of accurate interpretation to avoid errors in subsequent work.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the interpretation of the notation, with multiple competing views regarding the nature of N and its implications for the union of sets.

Contextual Notes

There are limitations regarding the assumptions about N, including its potential to be finite, countably infinite, or uncountable, which affects the interpretation of the union.

Asphodel
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I have something like this:

[tex]\bigcup^{N}_{1}x_{n}[/tex]

What am I looking at? Is this [tex]x_{1}\cup x_{2}\cup x_{3}\cup ...\cup x_{N}[/tex]?
 
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Yes, it's a union over some collection of sets.
 
Not necessarily because N can be infinite say...

x1 U x2 U x3 U ...

But also, N can be uncountable, which means listing them in whatever way is pointless and incorrect.
 
Thanks, Folland started using it without prior explanation (that I noticed).

It's the only interpretation that I could think of that made sense, but I didn't want to guess since it's already part of one theorem and one definition and if I guessed wrong then everything I did using those could be thrown off.
 

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