Each of the following exercises presents a flawless formal proof of validity for the indicated argument. For each proof, state the justification for each inferred statement (i.e., each statement that is not a premise).

1. (A ꓦ B) ⊃ C
2. (C ꓦ B) ⊃ [A . (D ≡ E)]
3. A ⋅ D
∴ D ≡ E
4. A
5. A ꓦ B
6. C
7. C ꓦ B
8. A ⊃ (D ≡ C)
9. D ≡ E