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Heron Suit
06-01-2015, 08:45 AM
Post: #9
RE: Heron Suit
(05-30-2015 06:32 PM)Dave Britten Wrote:  
Quote:No cats have tails unless they have whiskers.
Native English speaker here - from the UK, as is Ian Stewart. Looks like I agree with your analysis:
Quote:No cats have tails unless they have whiskers.
(I agree with the earlier poster that "unless" means "if not" - but it is one of the easiest logical words to misapprehend.)
Let me rewrite a few times:
Quote:All cats are without tails unless they have whiskers.
Quote:if a cat is without whiskers, it will be without a tail.
Quote:no whiskers => no tail.
Quote:tail => whiskers
Quote:tail and no whiskers never happens
which invalidates Stewart's counterexample.

According to http://www.cs.nott.ac.uk/~vxc/g51mcs/ch01_logic.pdf
Quote:No cats have tails unless they have whiskers.
is equivalent to
Quote:(Not tailed) OR whiskered
which we can transform to
Quote:Not (tailed AND not whiskered)
which is the same interpretation, I think.

That pdf concludes that the deduction is correct, and gives a derivation.
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Messages In This Thread
Heron Suit - Dave Britten - 05-30-2015, 06:32 PM
RE: Heron Suit - Gerald H - 05-30-2015, 07:02 PM
RE: Heron Suit - Dave Britten - 05-30-2015, 08:01 PM
RE: Heron Suit - Gerald H - 05-31-2015, 07:19 AM
RE: Heron Suit - Thomas Radtke - 05-31-2015, 10:35 AM
RE: Heron Suit - Bill (Smithville NJ) - 05-31-2015, 12:21 PM
RE: Heron Suit - Dave Britten - 05-31-2015, 05:21 PM
RE: Heron Suit - Thomas Radtke - 06-01-2015, 05:12 AM
RE: Heron Suit - Dave Britten - 06-01-2015, 11:03 AM
RE: Heron Suit - EdS2 - 06-01-2015 08:45 AM



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