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 Exercise Three: 3.1 - 3.2 - 3.3
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Exercise 3.1

 

1.

Which of the following sequents is correct? Where the sequent is incorrect, give a counterexample.
  (i) ¬[P®Q] |= [¬P®Q]
  (ii) ¬[P®Q] |= [P®¬Q]
  (iii) [P®Q] |= ¬[P®¬Q]
  (iv) [P®Q], [R®Q] |= [[PÚR]®Q]
  (v) [[P®Q]Ú [R®Q]] |= [[PÚR]®Q]
  (vi) |= [[P®Q]«[¬P®¬Q]]
  (vii) |= [[P®Q]«[¬Q®¬P]]
  (viii)  [PÙ¬P] |= Q
  (ix) Q |= [P®P]
Answers

 

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