Fixed some typos: ans

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Ok, I have finished them.

The hardest part about the four problems is to find the cycles of dihedral groups. After you figure that out, there is no difficulty at all. (Make good use of the property of prime number, and always try simple examples when you are stuck)

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The system requires me to finish the questions in 3 hours, but I just spent quite a while talking to you and haven’t finished the problems, so I will submit a blank file here and fill things up later.