Incorrect Answer.
To violate the relationship
(p 
q) 
r, 
r 
p 
q, we need a valuation that
makes p q false and
(p q) r and r true. For former forces p and q
to evaluate to F. The latter forces r to compute to F. Thus, there can only
be one valuation that witnesses a violation of the claimed semantic
entailment; the one that assign F to all atoms involved. This renders a
legitimate witness:
| p |
q |
r |
|
|
p q r |
r |
p q |
| F |
F |
F |
|
|
T |
T |
F |
The premises are both true, but the conclusion is false.
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