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Which of the following pairs of statements correctly represent a logical dual?

1. (p OR q) AND (r OR s), (p AND q) OR (r AND s)
2. [p OR (NOT q) AND (NOT p)] AND (NOT q) OR (NOT p)
3. (p AND q) OR r, (p OR q) AND r
4. (p OR q) OR s, AND (p AND q) OR s

Correct answer: (p AND q) OR r, (p OR q) AND r

Solution

The pair of statements (p AND q) OR r and (p OR q) AND r are logical duals because they have the same structure but with the operators AND and OR interchanged.

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