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Of all the connectives we've seen, the implication “$\rightarrow$” connective is probably the trickiest. Let $F$ and $G$ be two propositional formulas, over same set of propositional variables, such that $(F \rightarrow G)$ and $(G \rightarrow F)$ are equivalent. Which of the following is/are True?
  1. $(F \rightarrow G)$ is necessarily a Tautology.
  2. $(G \rightarrow F)$ is necessarily a Tautology.
  3. $(F \rightarrow G)\wedge (G \rightarrow F)$ is necessarily a Tautology.
  4. $F$ is necessarily equivalent to $G.$
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        F

        G

     F -> G

     G -> F

False

False

True

True

False

True

True

False

True

False

False

True

True

True

True

True

 

So we can see F→ G and G→ F become equivalent only F and G are both True or both False. So option (D) is correct. Now from option D, we can see (F→ G) ^ (G → F) gives True in both cases. So it is a tautology. So the answers are options (C) & (D).

 

Ans--- (C), (D)

Answer:

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