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Math Help - proofs please help

  1. #1
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    proofs please help

    Which of these statements are believable??

    a) "All of my 5-legged dogs can fly."
    b) "I have no 5-legged dog that cannot fly."
    c) "Some of my 5-legged dogs cannot fly."
    d) "I have a 5-legged dog that cannot fly."



    I think its (a) and (d), but im not sure. thanks.
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  2. #2
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    Quote Originally Posted by demon1 View Post
    Which of these statements are believable??

    a) "All of my 5-legged dogs can fly."
    Let me do the first one.

    It is saying "If there is a 5-legged man, than he flies."

    THe conditional is always false.

    Thus, the statement is always true.
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  3. #3
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    Quote Originally Posted by demon1 View Post
    Which of these statements are believable??

    a) "All of my 5-legged dogs can fly."
    b) "I have no 5-legged dog that cannot fly."
    c) "Some of my 5-legged dogs cannot fly."
    d) "I have a 5-legged dog that cannot fly."



    I think its (a) and (d), but im not sure. thanks.
    a) As you cannot producea 5-legged dog which cannot fly as evidence
    against it. Alternativly this claims that the null set is a subset of the null set.

    b) Same as the first reason in a).

    c) and d) are not beleivable unless you can produce a five legged dog. That
    is they assert that the set of five legged dogs is non-null.

    RonL
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