Indicate which of the following well-formed formulae are valid:
1990
Indicate which of the following well-formed formulae are valid:
- A.
[(P ⇒ Q) ∧ (Q ⇒ R)] ⇒ (P ⇒ R)
- B.
(P ⇒ Q) ⇒ (¬P ⇒ ¬Q)
- C.
(P ∧ (¬P ∨ ¬Q)) ⇒ Q
- D.
(P ⇒ R) ∨ (Q ⇒ R) ⇒ ((P ∨ Q) ⇒ R)
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Correct answer: A
Option A is correct
Reasoning: This is a fundamental law of logic known as the Law of Syllogism (or transitivity of implication). It states that if P implies Q, and Q implies R, then P must imply R.
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