Characterization of almost PP-ring for three important classes of rings

13.May.2020

​A ring is called an almost pp− ring if the annihilator of each element of R is generated by its idempotents. We prove that for a ring R and an Abelian group G, if the group ring RG is an almost pp− ring then so is R, Moreover, if G is a finite Abelian group then |G| −1 ∈ R. Then we give a counter example to the converse of this. Also, we prove that RG is an almost pp−ring if and only if RH is an almost pp− ring for every subgroup H of G. It is proved that the polynomial ring R [x] is an almost pp− ring if and only if R is an almost pp− ring. Finally, we prove that the power series ring R [[x]]is an almost pp− ring if and only if for any two countable subsets S and T of R such that S ⊆ AnnR (T), there exists an idempotent e ∈ AnnR (T) such that b = be for all b ∈ S. Keywords: almost pp−ring, group ring, polynomial ring, power series ring​