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Math Help - a simple question about quantifier

  1. #1
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    a simple question about quantifier

    Does ~∃(x) A(x) equal to ∀(x) ~A(x)?
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  2. #2
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    Quote Originally Posted by questionboy View Post
    Does ~∃(x) A(x) equal to ∀(x) ~A(x)?

    In my screen the above appears as \sim\square (x)A(x) ...try using LaTeX to make things clearer.

    Tonio
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  3. #3
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    The question is whether {\sim}\exists (x)A\,(x) is equal to \forall(x)\,{\sim} A(x). The short answer is yes. More precisely, it depends on the definition of "equal". I would say that, since these are two different formulas, they are not equal but equivalent, meaning that they are true in the same interpretations, or that they are derivable from each other.
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