Cycles on the Moduli Space of Abelian Varieties

In this paper a number of results on cycles on the moduli space of principally polarized abelian varieties is presented. Results include a determination of the tautological ring, bounds on the order of torsion of the top Chern class $\lambda_g$ and a determination of the cycle classes of the Ekedahl-Oort stratification in characteristic $p$. It includes as special cases formulas for the classes of loci like the $p$-rank $\leq f$ locus or the $a$-number $\geq a$-locus. The results on the tautological ring are my own work, the results on the torsion of $\lambda_g$ and on the cycle classes of the Ekedahl-Oort stratification are joint work with Torsten Ekedahl and some of the results on curves are joint work with Carel Faber.Comment: Plain TeX, 22 pages; an erroneous lemma correcte

Counting curves over finite fields

This is a survey on recent results on counting of curves over finite fields. It reviews various results on the maximum number of points on a curve of genus g over a finite field of cardinality q, but the main emphasis is on results on the Euler characteristic of the cohomology of local systems on moduli spaces of curves of low genus and its implications for modular forms.Comment: 25 pages, to appear in Finite Fields and their Application

The coset weight distributions of certain BCH codes and a family of curves

We study the distribution of the number of rational points in a family of curves over a finite field of characteristic 2. This distribution determines the coset weight distribution of a certain BCH code.Comment: Plain Tex, 15 pages; some numerical data adde

Kummer Covers with Many Points

We give a method for constructing Kummer covers with many points over finite fields.Comment: Plain Tex, 13 page

On the Existence of Supersingular Curves of Given Genus

We give a method to construct explicitly a supersingular curve of given genus g in characteristic 2.Comment: 9 pages, plain TeX, UvA-report 94-1