A generalization of Baker's theorem

  • Authors:
  • Peter Beelen

  • Affiliations:
  • Department of Mathematics, Technical University of Denmark, Matematiktorvet, Building 303S, DK 2800 Kgs. Lyngby, Denmark

  • Venue:
  • Finite Fields and Their Applications
  • Year:
  • 2009

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Abstract

Baker's theorem is a theorem giving an upper-bound for the genus of a plane curve. It can be obtained by studying the Newton-polygon of the defining equation of the curve. In this paper we give a different proof of Baker's theorem not using Newton-polygon theory, but using elementary methods from the theory of function fields (Theorem 2.4). Also we state a generalization to several variables that can be used if a curve is defined by several bivariate polynomials that all have one variable in common (Theorem 3.3). As a side result, we obtain a partial explicit description of certain Riemann-Roch spaces, which is useful for applications in coding theory. We give several examples and compare the bound on the genus we obtain, with the bound obtained from Castelnuovo's inequality.