Ralf Fröberg: On differential operators of numerical semigroup rings

If S=< d_1,...,d_n>, then k[S]=k[t^{d_1},...,t^{d_n}] is the semigroup ring of S. We study the ring of differential operators on k[S], and its associated graded in the filtration induced by the order of differential operators. If I is an ideal in k[S] generated by monomials,  we also give some results on Der(I,I), the set of derivations which map I into I. This is joint work with Valentina Barucci, Universita di Roma 1.