View Single Post
Jan14-07, 09:08 PM
P: 1
1. The problem statement, all variables and given/known data

I don't have symbols for negations, so i'll just use the word NOT..

Prove the validity of the sequents below:

NOT ( P -> Q) YIELDS Q-> P

2. Relevant equations

Relavent deductions as listed here..

Using things such as ^ elimination/introduction, Modens Ponens,.. etc

3. The attempt at a solution

1. NOT ( P -> Q) Premise
2. NOT Q Assumption
3. NOT NOT P MT 1,2 (added in extra negation from line 1)
4. P NOT NOT Elimination
5. NOT Q -> P

I"m looking for Q -> P.. which the opposite answer.. i think its something to do with the negations being all wrong.. any help??
Phys.Org News Partner Science news on
'Smart material' chin strap harvests energy from chewing
King Richard III died painfully on battlefield
Capturing ancient Maya sites from both a rat's and a 'bat's eye view'