August 27th, 2011, 10:33 AM  #1 
Newbie Joined: Aug 2010 Posts: 1 Thanks: 0  Sets under union
can some give me a example as well as prove of this Prove that Regular Sets are NOT closed under infinite union. (A counterexample suffices). 
August 27th, 2011, 01:01 PM  #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 under union
What have you tried so far? I would usually look at some languages that you know aren't regular to see if I can form them as an infinite union of regular languages. Actually, you should be able to do this for any nonregular language.


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