Mathematical Research Letters

Volume 11, Issue 6, November 2004 pp. 799-808.

Even sets of four nodes on rational surfaces

Authors: Alberto Calabri, Ciro Ciliberto and Margarida Mendes Lopes
Author institution: Università degli Studi di Bologna, Università degli Studi di Roma ``Tor Vergata'', and Instituto Superior Técnico

Summary: We describe smooth rational projective algebraic surfaces $X$, over an algebraically closed field of characteristic different from $2$, having an even set of four disjoint $(-2)$-curves $N_1,\ldots,N_4$, i.e. such that $N_1+\cdots+N_4$ is divisible by 2 in $\Pic(X)$.

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