Computing multi-point Seshadri constants on P2

Abstract

Working over the complex field and formalizing and sharpening approaches introduced by several authors, we give a method for verifying when a divisor on a blow up of P^2 at general points is nef. The method is useful both theoretically and when doing computer computations. The main application is to obtain significantly improved explicit lower bounds for multipoint Seshadri constants on P^2.

This is a shortened version (13 pp) of the original paper. Some of the results in the original paper have been generalized and are included in a new paper: arXiv:0709.3937