April 1st, 2010, 09:55 PM  #1 
Newbie Joined: Jan 2009 Posts: 7 Thanks: 0  sets theroy question
could someone help me with the proof of following in the sets theory A?(B?C) = (A?B)?C 
April 2nd, 2010, 06:25 AM  #2 
Global Moderator Joined: Nov 2006 From: UTC 5 Posts: 16,046 Thanks: 938 Math Focus: Number theory, computational mathematics, combinatorics, FOM, symbolic logic, TCS, algorithms  Re: sets theroy question
What does the delta mean?

April 2nd, 2010, 06:29 AM  #3 
Senior Member Joined: Nov 2008 Posts: 199 Thanks: 0  Re: sets theroy question
Ok, I'm going to write s instead of . x in As(BsC) iff either 1) x in A and x not in BsC or 2) x in BsC and x notin A. suppose 1). Then as x not in BsC either a) x not in B or C, or b) x in B and C. If a) then x in AsB and x not in C. If b) then x in C and x not in AsB. Either way x in (AsB)sC. To complete the proof you need to work out what happens when 2) holds and then use a similar method to show the inclusion the other way. p.s. is the symmetric difference. . 
April 3rd, 2010, 03:46 AM  #4 
Newbie Joined: Jan 2009 Posts: 7 Thanks: 0  Re: sets theroy question
thanks alot 

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