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I want to prove it, but don't know how... (I've tried to resolve complement by defining characteristic function like this: $\chi_{\bar A} = 1 - \chi_A$) Any ideas please? :-)

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    Why do you think it's true in the first place?2012-12-04
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    Actually I don't know if it is true, I just don't know how to start with proving/disproving ...2012-12-04
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    "r. (r.e.)"?${}$2012-12-04
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    recursive, recursively enumerable2012-12-04
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    The answer is not the same in those two cases.2012-12-04
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    if I define it like this: $\chi_{A * B} = \chi_A + \chi_B - 2\chi_{A \cap B}$ - then is it enough to proof that this char. function is $\mu$-recursive ? and then I can say, symmetric difference is recursive ?2012-12-04
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    If the claim were true of two recursively enumerable sets, then every r.e. set would be recursive.2012-12-04

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