Consider the following expressions: (i) \(false\) (ii) \(Q\) (iii) \(true\)…
2016
Consider the following expressions:
(i) \(false\)
(ii) \(Q\)
(iii) \(true\)
(iv) \(P∨Q\)
(v) \(¬Q∨P\)
The number of expressions given above that are logically implied by \(P ∧ (P ⇒ Q)\) is .
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Correct answer: 4
Key insight: From P ∧ (P ⇒ Q) we have both P and P ⇒ Q, so by modus ponens we can infer Q.
false — Not implied. The premises are satisfiable (they can be true), so they do not entail a contradiction.
Q — Implied, because from P and P ⇒ Q we derive Q by modus ponens.
true — Implied. A tautology is true in every model, so it holds in all models of the premises.
P ∨ Q — Implied, since P is true under the premises, making the disjunction true.
¬Q ∨ P — Implied, because P is true under the premises, so this disjunction is true.
Conclusion: Four of the given expressions are logically implied by P ∧ (P ⇒ Q).
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