By definition of ?, it even suffices to see that t ell,reg (F ) G ? p(F ) = ?. But this follows immediately from the fact that P being proper ,
Harmonic analysis on reductive p-adic groups. Notes by G. van Dijk Existence of cuspidal representations of p-adic reductive groups, Lecture Notes in Mathematics, vol.162, 1970. ,
Algebraic groups and number theory Translated from the 1991 Russian original by Rachel Rowen Représentations des groupes réductifs p-adiques Cours Spécialisés [Specialized Courses, Pure and Applied Mathematics, 1994. ,