  The goal of this paper is to present results which are consistent with
conjectures about the Leibniz (co)homology for discrete groups stated by J. L.
Loday. We show that rack cohomology has properties very close to the properties
expected for the conjectural Leibniz cohomology. In particular, we prove the
existence of a graded dendriform algebra structure on rack cohomology, and we
construct a graded associative algebra morphism from group cohomology to rack
cohomology which is injective in degree 1.
