D Question 7 Which among those are true? There exist formulas P and Q that are not equivalent and such that both P and Q are valid There exist formulas P and Q that are equivalent and such that P is...

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Extracted text: D Question 7 Which among those are true? There exist formulas P and Q that are not equivalent and such that both P and Q are valid There exist formulas P and Q that are equivalent and such that P is valid, while Q is not There exist formulas P and Q that are equivalent and such that both P and Q are not valid If both P and Q are valid then they are equivalent