# Thread: Equal power sets -> Equal sets?

1. ## Equal power sets -> Equal sets?

Hey guys, quick question, and I apologize if it's already been asked recently. But is it possible to prove two sets are equal if they have the same power sets? That is, can you say that A=B if A and B have the same power set?

I have a feeling the answer's no, but I can't think of an example where it wouldn't be true.

2. Originally Posted by Walcott89
Hey guys, quick question, and I apologize if it's already been asked recently. But is it possible to prove two sets are equal if they have the same power sets? That is, can you say that A=B if A and B have the same power set?

I have a feeling the answer's no, but I can't think of an example where it wouldn't be true.
It is easy to prove it true.
See this.

3. Thank you, Plato!

4. ## Re: Equal power sets -> Equal sets?

I am trying to find the link for equal power sets, but it returns me to home page. Any suggestions.

5. ## Re: Equal power sets -> Equal sets?

Originally Posted by cpcook
I am trying to find the link for equal power sets, but it returns me to home page. Any suggestions.
That is a very old reply, almost three years ago. The link is no longer active.
If I were you I start a new thread to ask whatever question(s) you have about power sets.

6. ## Re: Equal power sets -> Equal sets?

If two sets, X and Y, have the same power sets (the power set of set A is the collection of all subsets of A) then the singleton sets in the power sets must be the same. But X is just equal to the union of all singleton sets in the power set of X and Y is the union of all singleton sets in the power set of Y.

7. ## Re: Equal power sets -> Equal sets?

Or seeing it slightly differently; since A and B have the same powersets (thus they have the same subsets) and every set is a subset of itself, $A \subseteq B$ and $B \subseteq A$, so $A = B$

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# power set are equal then set also equal

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