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Exercise 2.1.10 (Isometry Cube)
Example 2.1.9(iii) shows that the action of the isometry group of the cube on the set of long diagonals is not faithful. By Lemma 2.1.8, there must be some non-identity isometry of the cube that fixes all four long diagonals. In fact, there is exactly one. What is it?
Answers
The symmetry relative to the center of the cube preserves each of the four long diagonals, and is a non-identity isometry.