A geometric approach to the Cohen-Lenstra heuristics

For any positive integer $n$, we explain why the total number of order $n$ elements in class groups of quadratic fields of discriminant having absolute value at most $X$ is $O_n(X^{5/4})$.

Zoom: https://harvard.zoom.us/j/96767001802

Password: The order of the permutation group on 9 elements.