Harder's denominator problem for ${\mathrm{SL}}_2(\mathbb{Z})$ and its applications

Hohto Bekki, Ryotaro Sakamoto

The aim of this paper is to give a full detail of the proof given by Harder of a theorem on the denominator of the Eisenstein class for ${\mathrm{SL}}_2(\mathbb{Z})$ and to show that…