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Is this an example of entailment? Does A entail B?

A. None of Bob's friends have visited Africa. B. None of Bob's friends have visited Kenya.

But B seems to survive of A is negated: A'. Some of B's friends have visited Africa, but none have visited Kenya.

This does not seem like a contradiction.

Can someone shed some light on this question?

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  • B entails A, not the other way round. – curiousdannii Apr 4 '16 at 6:17
  • Negation changes the relationship. – jlawler Apr 4 '16 at 14:39
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First we negate both sentences to see which one entails the other:

Some of Bob's friends have visited Kenya Therefore Some of them have visited Africa

This shows that B entails A. Let's see if it is true the other way around

Some of Bob's friends have visited Africa Therefore They may or may not have visited Kenya.

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