About the group law for the Jacobi variety of a hyperelliptic curve
arXiv:math/0509638
Abstract
We generalize the group law of curves of degree three by chords and tangents to the Jacobi variety of a hyperelliptic curve. In the case of genus 2 we accomplish the construction by a cubic parabola. We derive explicit rational formulas for the addition on a dense set in the Jacobian.
5 pages