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Exercises 5.4 number 1g (page 353)

Posted by hexium

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hexium

Exercises 5.4 number 1g (page 353)
May 30, 2011 10:46AM

Registered: 16 years ago
Posts: 111
Rating: 0

Hey slow_eddy,
This question has me stumped. Do you know what to make of it?

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Tazz

Re: Exercises 5.4 number 1g (page 353)
May 30, 2011 12:03PM

Registered: 13 years ago
Posts: 363
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I'm attempting this q at the moment and to be quite honest I am stuck at line 2! Don't even know what step to take after line 1!

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hexium

Re: Exercises 5.4 number 1g (page 353)
May 30, 2011 12:40PM

Registered: 16 years ago
Posts: 111
Rating: 0

I thought that maybe if I started with an assumption []~p, I could somehow prove a contradiction and conclude ~[]~p, from where I could use disjunction introduction to get to the answer... but it did not take me anywhere.. this is a particularly tough one.. I'm obviously missing something small...

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slow_eddy

Re: Exercises 5.4 number 1g (page 353)
May 30, 2011 02:10PM

Registered: 15 years ago
Posts: 3,496
Rating: 1

For the time being all I can say is it rings a bell... Yes, it has a similar form to the one from the exam (apart from the connective). I'll have to go bash away at it, and see whether I can find a way...

I think we go into the arbitrary world, and then reason in an ordinary way? So pick a target inside there that comes out as ... hmm. OK if the only thing that came out was diamond p, surely one could then conclude "diamond-p OR absolutely-anything" ?

Or is that stretching OR-i too far?