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Daniele Zuddas
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Very symmetric quadrangle in $\Bbb CP^2$

Is there a quadrangle $Q \subset \Bbb CP^2$, namely $Q$ is a set of four points, such that every permutation of $Q$ can be realizable by an isometric projectivity of $\Bbb CP^2$? Clearly the analogous question for a triangle in $\Bbb CP^1 \cong S^2$ has affirmative answer: it is a maximal equilateral triangle. More generally, is there a subset of $n+2$ points in $\Bbb CP^n$ such that all of its permutations are restrictions of some isometric projectivity?

Daniele Zuddas
  • 2.3k
  • 13
  • 19