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Hardly understand derivations at all

 
 
mgib-2
 
Reply Sat 26 Jan, 2013 10:15 pm
give a direct derivation: P→(Q→R). (Q→R)→S. ∼S ∴ ∼P
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Type: Question • Score: 0 • Views: 1,270 • Replies: 3
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markr
 
  2  
Reply Sun 27 Jan, 2013 01:19 pm
@mgib-2,
After looking up direct derivation, it seems you want this:

1) P→(Q→R)
2) (Q→R)→S
3) ∼S
4) show ∼P
---------------
5) ~(Q→R).........2,3,→O
6) ~P..................1,5,→O
mgib-2
 
  1  
Reply Sun 27 Jan, 2013 01:32 pm
@markr,
Im not exactly sure what →O means. I've entered it into the problem but it says that there is no rule named that. If you could tell me what you mean by →O I could probably figure out what to put in the problem.
markr
 
  1  
Reply Sun 27 Jan, 2013 02:03 pm
@mgib-2,
Look at page 162 of this:
http://courses.umass.edu/phil110-gmh/text/c05_3-99.pdf
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