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Which of the following pairs is NOT a correct dual pair?

1. (p∨q)∧(r∨s), (p∧q)∨(r∧s)
2. [p∨(~q)]∧(~p), [p∧(~q)]∨(~p)
3. (p∧q)∨r, (p∨q)∧r
4. (p∨q)∨s, (p∧q)∨s

Correct answer: (p∨q)∨s, (p∧q)∨s

Solution

The dual is obtained by interchanging ^ and v. The dual of (p v q) v s is (p ^ q) ^ s, but option D lists (p ^ q) v s, so this pair is NOT a correct dual pair.

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