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 .

Attempted by 107 students.

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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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