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These are some examples in modal logic, I am not too sure why the first two are valid and why the last one specifically is not valid. Hope someone can explain!

  1. $\square(P \rightarrow P)$ (VALID)

  2. $\square P \rightarrow \square P$ (VALID)

  3. $\square P \rightarrow P$ (NOT VALID)

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    Your question shows up with square boxes at the beginning of each statement, so I don't know what it actually says. You may want to consider using LaTeX to write out the math.2012-12-06
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    @JonathanChristensen: I hope the edits have made everything clear!2012-12-06

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