 
Summary: Unipotent Automorphic Representations:
Global Motivation
JAMES ARTHUR
Contents
§1. Introduction . . . . . . . . . . . . . . . . . . . . . 1
§2. Endoscopic data .................. . 5
§3. The discrete part of the trace formula .......... 14
§4. The conjectural multiplicity formula ..... ..... 20
§5. The expansion of Idisc,t(f) ............... 27
§6. The sign characters e, and r.............. 37
§7. The expansion of Edis,t(f) ............... 42
§8. A combinatorial formula for Weyl groups ......... 54
§9. Concluding remarks .................. 67
§1. INTRODUCTION
In the paper [3], we gave a conjectural description of the discrete
spectrum attached to the automorphic forms on a general reductive
group. The main qualitative feature of this description was a Jordan
decomposition into semisimple and unipotent constituents. This is in
keeping with the dual nature of conjugacy classes and characters, and
in fact, with a general parallelism between geometric objects and spec
