4.2.x. Exercises
1. |
Use derivations to establish each of the claims of entailment and equivalence shown below. (Remember that claims of equivalence require derivations in both directions.) |
|
a. | A ∧ B ⇒ A ∨ B | |
b. | A ∧ B ⇒ B ∨ C | |
c. | A ∨ B, ¬ A ⇒ B | |
d. | A ∨ (A ∧ B) ⇒ A | |
e. | A ∨ B, ¬ (A ∧ C), ¬ (B ∧ C) ⇒ ¬ C | |
f. | A ∧ (B ∨ C) ⇒ (A ∧ B) ∨ C | |
g. | A ∨ B, C ⇒ (A ∧ C) ∨ (B ∧ C) | |
h. | A ∨ B, ¬ A ∨ C ⇒ B ∨ C | |
i. | A ⇔ (A ∧ B) ∨ (A ∧ ¬ B) |
2. |
Use derivations to establish each of the claims of equivalence below. | |
a. | A ∨ A ⇔ A | |
b. | A ∨ B ⇔ B ∨ A | |
c. | A ∨ (B ∨ C) ⇔ (A ∨ B) ∨ C | |
d. | A ∨ (B ∧ ¬ B) ⇔ A | |
e. | ¬ (A ∨ B) ⇔ ¬ A ∧ ¬ B | |
f. | ¬ (A ∧ B) ⇔ ¬ A ∨ ¬ B |
3. |
Use derivations to check each of the claims below; if a derivation indicates that a claim fails, present a counterexample that divides an open gap. |
|
a. | A ∨ B, A ⇒ ¬ B | |
b. | A ∨ (B ∧ C) ⇔ (A ∨ B) ∧ C | |
c. | ¬ (A ∨ B) ⇔ ¬ A ∨ ¬ B |