1) Construct derivations that establish the following derivability claims.

a)    {~ A ⊃ ~ B, A ⊃ C, B ∨ D, D ⊃ E} ⊢ E ∨ C

b)     {~ A ⊃ B, C ⊃ ~ B, ~ (~ C & ~ A)} ⊢ A

2) Show that the following set of sentence of SL is inconsistent in SD.

a) {B ≡ (A & ~ A), ~ B ⊃ (A & ~ A)}

3) Prove the equivalent below:

P⊃ (Q ⊃ P) and (~Q ⊃ (P ⊃ (~Q V P)))