Use your newly gained natural deduction skills to solve the following problems. In each problem, the
arrow symbol means the same thing as the horseshoe symbol in the preceding chapter.

9.
1. ~G→(G ∨ ~A)
2. ~A→(C→A)
3. ~G /~C

10.
1. G→[~O→(G→D)]
2. O ∨ G
3. ~O /D

11.
1. ~N ∨ (C ∨ ~U)
2. C → X
3. ~ ~ N
4. ~X /~U

12.
1. G → [~D → (B → ~C)
2. ~C → D
3. D ∨ G
4. ~D / ~B

13.
1. (C→M) → (N→P)
2. (C→N) → (N→M)
3. (C→P) → ~M
4. C→N /~C

pur-new-sol