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  1. GATE CS
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  3. Discrete Mathematics

The binary operation □ is defined as follows: P | Q | P □ Q T | T | T T | F | F F | T | T F | F | T Which one of the following is equivalent to P □ Q? A. ~(C -> P) B. ~(P ^ ~Q) C. P ^ Q D. ~P ^ Q

GATE 2009 · Discrete Mathematics · Propositional Logic · easy

Answer: P □ Q is equivalent to P -> Q = ~(P ^ ~Q), so the answer is B.

  1. Read the operation's truth table: P □ Q gives T,F,T,T for rows (T,T),(T,F),(F,T),(F,F). Compare with P -> Q: T,F,T,T. They match exactly. So P □ Q = P -> Q.
  2. Express implication as ~(P ^ ~Q) using De Morgan: P -> Q = ~P v Q. Apply De Morgan in reverse: ~P v Q = ~(~~P ^ ~Q) = ~(P ^ ~Q). So option B = ~(P ^ ~Q) is equivalent to P □ Q.