Continuity set

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In classical algebraic geometry, the genus–degree formula relates the degree d of a non-singular plane curve C2 with its arithmetic genus g via the formula:

g=12(d1)(d2).

A singularity of order r decreases the genus by 12r(r1).[1]

Proof

The proof follows immediately from the adjunction formula. For a classical proof see the book of Arbarello, Cornalba, Griffiths and Harris.

Generalization

For a non-singular hypersurface H of degree d in n of arithmetic genus g the formula becomes:

g=(d1n),

where (d1n) is the binomial coefficient.

Notes

  1. Semple and Roth, Introduction to Algebraic Geometry, Oxford University Press (repr.1985) ISBN 0-19-85336-2. Pp. 53–54

References

  • Template:Citizendium
  • Arbarello, Cornalba, Griffiths, Harris. Geometry of algebraic curves. vol 1 Springer, ISBN 0-387-90997-4, appendix A.
  • Grffiths and Harris, Principles of algebraic geometry, Wiley, ISBN 0-471-05059-8, chapter 2, section 1
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