The Complete Intersection Discrepancy of a Curve I: Numerical Invariants

Abstract

We generalize two classical formulas for complete intersection curves by introducing the complete intersection discrepancy of a curve as a correction term. The first is a well-known multiplicity formula in singularity theory, due to Lê, Greuel and Teissier, which relates some of the basic invariants of a curve singularity. We apply this generalization elsewhere to the study of equisingularity of curves. The second is the genus--degree formula for projective curves. The main technical tool used to obtain these generalizations is an adjunction-type identity derived from Grothendieck duality theory.

With an appendix by Marc Chardin. Accepted for publication in Transactions of the American Mathematical Society