282 Logic as a Tool (d) [p]1 p ∨ ¬p [¬(p ∨ ¬p)] ⊥ ¬p (f) ND [p] [¬p]2 p ∨ ¬p ⊥ p ∨ ¬p [¬(p ∨ ¬p)] ⊥ ¬¬p ((p → q ) ∧ (p → ¬q )) → ¬p: [(p → q) ∧ (p → ¬q)] p→q q [p] ⊥ ¬p ((p → q) ∧ (p → ¬q)) → ¬p 2.4.4 (a) Suppose A ND B [A]1 ¬B , B ⊥ ¬A Hence ¬B ND ¬A (b) Suppose ¬B ND ¬A [¬B]1 A, ⊥ B Hence A ND B ¬A [(p → q) ∧ (p → ¬q)] p → ¬q ¬q 2