# Equal power sets -> Equal sets?

• Sep 21st 2009, 09:20 AM
Walcott89
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.
• Sep 21st 2009, 09:36 AM
Plato
Quote:

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.
• Sep 21st 2009, 09:55 AM
Walcott89
Thank you, Plato!
• Jun 29th 2012, 08:44 AM
cpcook
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.
• Jun 29th 2012, 08:51 AM
Plato
Re: Equal power sets -> Equal sets?
Quote:

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 The link is no longer active.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.
• Jun 29th 2012, 11:39 AM
HallsofIvy
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.
• Jul 5th 2012, 09:23 AM
thesmurfmaster
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, \$\displaystyle A \subseteq B\$ and \$\displaystyle B \subseteq A\$, so \$\displaystyle A = B\$