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Why the 2-shpere S^2 and the procective plane RP^2 are not diffeomorphic?

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I suspect that this is homework. If so, I suggest you think about any tools which you have learned to distinguish one space from another; most of them will work here. In case I am wrong, I'll throw out some buzzwords: fundamental group, orientability, homology. Any of these tools will work. – David Speyer Oct 21 2009 at 19:28
A clarification on what we're taking "too localized" to mean. This reason for closing generally means that the question is obviously a homework question and the asker doesn't give any indication that he has thought about the problem. Such questions offend the sensibilities of mathematicians. – Anton Geraschenko♦ Oct 21 2009 at 20:17
you are both right. I haven't thought much about it . i apologise – student Oct 22 2009 at 21:08

closed as too localized by David Zureick-Brown♦ Oct 21 2009 at 19:41

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