Even sets of four nodes on rational surfaces

Alberto Calabri, Ciro Ciliberto, Margarida Mendes Lopes
2004 Mathematical Research Letters  
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 , . . . , N 4 , i.e. such that N 1 + · · · + N 4 is divisible by 2 in Pic(X).
doi:10.4310/mrl.2004.v11.n6.a7 fatcat:ug726igjnve35pdnqwifskldhu