Seminar

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A numerical semigroup S is a cofinite subset of the non-negative integers, containing 0 and closed under addition. They arise as value semigroups of 1-dimensional singularities, as Weierstrass semigroups of points on smooth curves, and the associated semigroup rings form a pleasantly simple family of examples of 1-dimensional domains. 

The smallest nonzero element is called the multiplicity, m(S). Kunz showed that the numerical semigroups of multiplicity m can be represented as the lattice points in a convex rational cone in QQ^(m-1), now called the Kunz cone; and that many properties of the semigroup ring are determined by the face of the Kunz cone on which the semigroup lies.

I'll describe the Kunz cone and some of the still-open problems about semigroup rings that might be studied using it.