In this paper, coincidence formulas for Lefschetz numbers of twisted Hecke operators acting on the cohomology of arithmetic groups are calculated by using topological methods. These methods are of the same type as those used commonly in order to prove Lefschetz fixed point formulas.

First the author constructs the Hecke operation by defining it on cochain level. Thus he obtains the first coincidence formula in terms of adeles as follows: Let G be a reductive group over $\mathbb{Q}$ with arbitrary $\mathbb{Q}$-rank and trivial character group over $\mathbb{Q}$, $\tau$ a G- automorphism of finite order and $\alpha \in G\left({𝔸}_f\right)$. For every system $\tilde{M}$ of local coefficients one obtains the following formula:

The numbers J($\xi )$ depend only on the $\tau$- conjugation class of $\xi$ and do not disappear save in a finite number of cases, and in these cases the orbital integral converges.

Afterwards the author proves explicit formulas for $\mathbb{Q}$-rank one by decomposing $L\left(T_{\alpha }{\tau }^{*-1}\right)$ in an elliptic part $L_e$ (being a sum of Euler characteristics) and a boundary part $L_{\partial }$ induced by a correspondence on the boundary of the Borel-Serre compactification. As a consequence of these formulas one obtains some well known class number relations.