| Phi 270 Fall 2013 |
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3.4.x. Exercise questions
| 1. |
The following arguments are not formally valid. In each case, use a derivation to show this and confirm a counterexample that the derivation leads you to. |
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| a. | ¬ B / ¬ (A ∧ ¬ B) | |
| b. | ¬ (A ∧ B) / ¬ A ∧ ¬ B | |
| c. | ¬ (A ∧ B), ¬ (B ∧ C) / ¬ (A ∧ C) | |
| 2. |
Use derivations to check the following claims of entailment. If the claim fails, confirm a counterexample that the derivation leads you to. |
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| a. | ¬ (A ∧ ¬ B) ⊨ B | |
| b. | ¬ (A ∧ B) ⊨ ¬ (B ∧ A) | |
| c. | ¬ (A ∧ ¬ B) ⊨ ¬ (B ∧ ¬ A) | |
| d. | ¬ (A ∧ B), ¬ (B ∧ C), B ⊨ ¬ A ∧ ¬ C | |
| e. | ¬ (A ∧ ¬ (B ∧ ¬ (C ∧ ¬ D))) ⊨ ¬ (A ∧ ¬ (B ∧ D)) | |
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