Invariante Spuren auf Gruppenalgebren.
In this paper we extend the result established for the euclidean space in [3] to the hyperbolic disk. This includes the reconstruction of a function defined in a fixed disk B(0,R) from its averages on disks of radii r1, r2 lying in B(0, R).
Let L¹(G)** be the second dual of the group algebra L¹(G) of a locally compact group G. We study the question of involutions on L¹(G)**. A new class of subamenable groups is introduced which is universal for all groups. There is no involution on L¹(G)** for a subamenable group G.