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I'm not exactly sure how to go about this.

Thanks

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Is this maybe a StackOverflow question? Please show what you need it for, and what you have tried so far. –  Hidde Feb 20 '12 at 20:58
    
No, this wouldn't be a StackOverflow question. I just need to show the expression which expresses the alphabet $(a, b, c)$ using the language I have mentioned above. I'm not sure how to do this, but i have done something like $(a|b|c|aaa|bbb|ccc)$ and so on, including every odd charactered combination. –  AkshaiShah Feb 20 '12 at 21:01

1 Answer 1

up vote 4 down vote accepted

Hint:

What language does $(aa)^*$ represent over the alphabet $\{a\}$?

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So would it be $a^*|b^*|c^*$? –  AkshaiShah Feb 20 '12 at 21:03
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What you have mentioned represents the language of all words that have even length. –  AkshaiShah Feb 20 '12 at 21:04
    
@akshai5050: No, $a*|b*|c*$ is not correct. You can verify it yourself, by trying out some sample strings. Yes to the second comment. –  Aryabhata Feb 20 '12 at 21:07
    
Yes, I now realise what I said wouldn't be correct, as even lettered words would also be accepted by the expression. So, would it then be $a(aa)^*|b(bb)^*|c(cc)^*$? –  AkshaiShah Feb 20 '12 at 21:10
    
@akshai5050: What about words like $abc$? You miss those, don't you? –  Aryabhata Feb 20 '12 at 21:13

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