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Genus-degree formula

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In classical algebraic geometry, the genus-degree formula relates the degree d of a plane curve C\subset\mathbb{P}^2 with its arithmetic genus g via the forumla:

g = (d − 1)(d − 2)

Proofs

The proof is immediate by adjunction. For a classical proof see the first reference below.

References

  • Arbarello, Cornalba, Griffiths, Harris. Geometry of algebraic curves. vol 1 Springer, ISBN 0387909974, appendix A.
  • Grffiths and Harris, Principls of algebraic geometry, Wiley, ISBN 0-471-05059-8, chapter 2, section 1
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