$$
0\to \mathscr O_{C_1\cup C_2} \to \mathscr O_{C_1}\oplus \mathscr O_{C_2} \to \mathscr O_{C_1\cap C_2} \to 0
$$
(with maps $a\mapsto (a,a)$ and $(a,b)\mapsto a-b$)
is exact and $\chi$ is additive.
|
2 | deleted 1 characters in body | ||
|
|
||||
|
|
1 |
|
||
|
$$
0\to \mathscr O_{C_1\cup C_2} \to \mathscr O_{C_1}\oplus \mathscr O_{C_2} \to \mathscr O_{C_1\cap C_2} \to 0
$$
(with maps $a\mapsto (a,a)$ and $(a,b)\mapsto a-b$) |
||||
