preprint available

My manuscript "Geometric Algebra of Projective Lines" is available at arXiv, http://arxiv.org/abs/1003.2095 It is a sequel to the preprint on "Abstract Projective Lines" posted in December 2009. Abstract: The projective line over a field carries structure of a groupoid with a certain correspondence between objects and arrows. We discuss to what extent the field can be reconstructed from the groupoid. (The *multiplication* of the field comes from the *composition* of the groupoid; the crux is to reconstruct the *additive* structure.) Anders Kock [For admin and other information see: http://www.mta.ca/~cat-dist/ ]