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A => B does not mean !B => !A. In US (culturally): "Good dental hygiene" => "You floss". So dentists looking in your mouth can guess if you floss. However in Europe flossing is not as common and the link breaks. All dentists can say is if you take good care of your mouth, not if you floss or not.


> A => B does not mean !B => !A.

Uh... yes, it does. See https://en.wikipedia.org/wiki/Contraposition


Sorry to be pedantic but A => B is equivalent to !B => !A . Still, I agree that US dentists overemphasize flossing.




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