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Oct 5, 2011 at 20:13 comment added mrw It seems quite easy to me. Assume that $\Gamma=\sum a_i \Gamma_i \equiv 0$ for some $a_i\in \mathbb N$ then $D+\Gamma^+\equiv D+\Gamma^-$, which implies the claim.
Oct 5, 2011 at 15:10 comment added Gianni Bello Actually I don't see it so trivially. Of course $N^1(X)$ is finitely generated, but how do you see that the $\Gamma_i$ (I'm using the notation of my previous comments ) are not linearly dependent? This requires some effort in Nakayama's book, I cannot see this in a trivial way.
Oct 5, 2011 at 2:04 vote accept Zhengyu Hu
Oct 5, 2011 at 2:04 comment added Zhengyu Hu This is correct. The finite generation of Neron-Severi group gives it.
Oct 4, 2011 at 19:26 history edited mrw CC BY-SA 3.0
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Oct 4, 2011 at 19:25 comment added mrw That is correct.
Oct 4, 2011 at 19:16 comment added Gianni Bello I reckon that to show the last assetion of your answer you need to use that if the $\Gamma_i$ are prime divisors such that $\sigma_{\Gamma_i}(D)>0$, then the numerical classes of the $\Gamma_i$ are linearly independent in the vector space $N^1(X)$. Am I wrong? This is what Nakayama does in his book.
Oct 4, 2011 at 19:00 comment added mrw I added two lines of explanations... let me know if it is clear.
Oct 4, 2011 at 18:56 comment added Gianni Bello How do you know that they remain a finite number when you pass to the limit?
Oct 4, 2011 at 18:49 history edited mrw CC BY-SA 3.0
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Oct 4, 2011 at 18:38 history answered mrw CC BY-SA 3.0