Central Idempotents in Group Rings

Source abstract

Let R be a ring and G a group. The group ring RG consists of all functions f : G → R with finite support. Addition is pointwise and multiplication is defined for f , h ∊ RG and g ∊ G , by The support group of f is defined to be the subgroup of G generated by the support of f . The element f is idempotent if ff = f We prove the following result.