Incorrect Answer.
Incorrect Answer.
q 
r, q 
r, since soundness of
propositional logic would then imply that p q r, q 
r holds as
well. But the latter is not true (recall Question 5); for if r is false, q is
true, and p is false, then p q r and q are true,
but the claimed consequence, r, is not.
However, can you prove the weaker sequent
p, p q r, q r?