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  1. \item \self Consider the propositional formula $\varphi = p \imp
  2. (q \imp r)$.
  3. \begin{enumerate}
  4. \item Fill out the truth table for $\varphi$ and its
  5. subformulas.
  6. \begin{tabular}{|c|c|c||c|c|c|}
  7. \hline
  8. $p$&$q$&$r$&$(q \imp r)$&$\varphi=p \imp (q \imp r)$\\
  9. \hline
  10. \hline
  11. \textbf{F} &\textbf{F} &\textbf{F} & \T & \T \\
  12. \hline
  13. \textbf{F} &\textbf{F} &\textbf{T} & \T & \T \\
  14. \hline
  15. \textbf{F} &\textbf{T} &\textbf{F} & \F & \T \\
  16. \hline
  17. \textbf{F} &\textbf{T} &\textbf{T} & \T & \T \\
  18. \hline
  19. \textbf{T} &\textbf{F} &\textbf{F} & \T & \T \\
  20. \hline
  21. \textbf{T} &\textbf{F} &\textbf{T} & \T & \T \\
  22. \hline
  23. \textbf{T} &\textbf{T} &\textbf{F} & \F & \F \\
  24. \hline
  25. \textbf{T} &\textbf{T} &\textbf{T} & \T & \T \\
  26. \hline
  27. \end{tabular}
  28. \item Is $\varphi$ satisfiable? \\
  29. \quad Yes.
  30. \item Give a formula $\psi$ that is semantically equivalent to
  31. $\varphi$, but does not use the ``$\imp$'' connective.
  32. \quad $\psi = \neg p \lor (\neg q \lor r)$
  33. \item How can you check whether $\psi$ is semantically equivalent
  34. to $\varphi$?
  35. \quad Since both formulas are relatives compact, we can use their respective truth table to check whether they are semantically equivalent. We do this by checking whether they evaluate to $\T$ under the same models.
  36. \end{enumerate}