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Valid inference step (assignment 1 Q2)

Posted by SCag

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SCag

Valid inference step (assignment 1 Q2)
April 11, 2010 04:54PM

Registered: 15 years ago
Posts: 1,563
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Are we allowed to use DeMorgan as a valid inference step?

I have an identity which would suite me changing with DeMorgans law, but I dont know if I am allowed to use "DeMorgan" as a reason, or if I have to put the whole DeMorgan proof in (This would be crap because it would increase the size of the proof by 5 times.)

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Re: Valid inference step (assignment 1 Q2)
April 12, 2010 09:44AM

Registered: 15 years ago
Posts: 133
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I have no idea, you would have to confirm this with a lecturer.

In my answers, I assumed that I could only use the rules of natural deduction listed in the textbook, ie all the ones on page 27.

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SCag

Re: Valid inference step (assignment 1 Q2)
April 12, 2010 10:31AM

Registered: 15 years ago
Posts: 1,563
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Ye but the thing is, DeMorgans laws can be proved with the laws of natural deduction. Its just that including that sub proof will increase the size of my proof by a lot :'<

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Re: Valid inference step (assignment 1 Q2)
April 12, 2010 10:40AM

Registered: 15 years ago
Posts: 133
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Do you really need them? My longest proof was 11 lines.

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Anonymous User

Re: Valid inference step (assignment 1 Q2)
April 12, 2010 10:41AM

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In my view you must be able to.

First do the proof for DeMorgan seperately (as the text book did for MT), and then you can refer to it. I think they will burn you for just using DeMorgan without 1st proving it.

If you're needing DeMorgan for 2.6 - you don't smile

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kiolb

Re: Valid inference step (assignment 1 Q2)
April 12, 2010 10:43AM

Registered: 16 years ago
Posts: 423
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Hopefully there is another way to solve it, as I did not use De Morgan for any of them.

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Anonymous User

Re: Valid inference step (assignment 1 Q2)
April 14, 2010 10:11PM

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Thought I'd give one of 'ol DeMorgan's equivalences a try in Fitch...