preprint available

My manuscript "Abstract Projective Lines" is available at arXiv, http://arxiv.org/abs/0912.0822 Abstract: We describe a notion of (abstract) projective line over a field as a set equipped with a certain first order structure, and a projectivity between projective lines as a bijection preserving this structure. The structure in question is that of a groupoid, with certain properties. This leads to a natural notion of bundle of projective lines, forming a stack. Anders Kock [For admin and other information see: http://www.mta.ca/~cat-dist/ ]