For each numbered statement that is not a premise in each of the formal proofs that follow, state the rule of inference that justifies it.

1. A ⊃ B
2. B ⊃ C
3. C ⊃ A
4. A ⊃ ~ C
∴ ~ A ⋅ ~ C
5. A ⊃ C
6. (A ⊃ C) ⋅ (C ⊃ A)
7. A ≡ C
8. (A ⋅ C) ꓦ (~ A ⋅ ~ C)
9. ~ A ꓦ ~ C
10. ~ (A ⋅ C)
11. ~ A ⋅ ~ C