Hi, Topologists/Geometers:(adsbygoogle = window.adsbygoogle || []).push({});

I am trying to show that CP^2 and CP^2-bar (meaning CP^2 with reverse choice of

orientation, are not diffeomorphic.

I am kind of rusty; all I can think of using is the intersection form, but I do not

remember the precise result that we can use to show this. I have checked Rohklin's

theorem and other results in intersection forms, without success.

I would appreciate your suggestions.

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# CP^2 , and CP^2 -bar, are not diffeomorphic.

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