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# Algebra of Sets Notation Question watch

1. Quick question, in set algebra what does the "/" mean? I seem to be missing my notes for this. See the following link for an example:

Click

Also, on the same image could you tell me what the following question means. I've not come across the U before either.

Thanks.
2. Don't ever ever ever ever ever ever write forward slash for that! I've had nightmares from constantly reminding someone at uni of this. / is used for something else. It's \ .

If A and B are sets then A\B is the set containing everything in A that's not contained in B. It's said "A excluding B".

U is the union. So AUB is the set containing everything in A or B.
n is the intersection. AnB is the set containing everything in both A and B
3. Thanks, and sorry about the "/".

I know the union and intersection, I was wondering what the large U is on the next line down of the link? Or is that some kind of union too?
4. (Original post by ironically)
Thanks, and sorry about the "/".

I know the union and intersection, I was wondering what the large U is on the next line down of the link? Or is that some kind of union too?
Ah. It just means ... U A(-1) U A0 U A1 U A2 U ... (it's over all integers here)
Kind of like summation notation.
5. Sorry, I don't quite follow...
6. Maybe it'll be clearer if I latex it:

You have a collection of sets

So in words, the union of all the as n varies over the integers. That's the set of all x that appear in for some n in the intergers.
7. Ah, thank you. That's much clearer.
8. what does / mean?
9. (Original post by Totally Tom)
what does / mean?
Division. But what complicates things is that there's no real meaning for division between arbitrary sets. On the other hand, there are a whole bunch of specialised scenarios where it does make sense, although the exact definition of "division" is going to change (a lot!) depending on the scenario.

This is why you really really don't want to mix up / and \.
10. (Original post by DFranklin)
Division. But what complicates things is that there's no real meaning for division between arbitrary sets. On the other hand, there are a whole bunch of specialised scenarios where it does make sense, although the exact definition of "division" is going to change (a lot!) depending on the scenario.

This is why you really really don't want to mix up / and \.
cool thanks

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