Idempotent Ideals in Perfect Rings

Abstract

All rings considered in this note have an identity element, and all R -modules are unitary. Bass ( 2 ) defined a left perfect ring as a ring R satisfying the minimum condition on principal right ideals. A commutative ring R is perfect if and only if R is a direct sum of finitely many local rings whose radicals are T -nilpotent. Therefore, the commutative perfect rings with finite global projective dimension are just the direct sums of finitely many commutative fields, and hence they trivially satisfy the minimum condition for all ideals. However, in the non-commutative case, even hereditary perfect rings are not necessarily right or left artinian (cf. Example 3.4). Each left perfect ring R has only finitely many idempotent (two-sided) ideals (Corollary 2.3), where the ideal X of R is called idempotent, if X = X 2 . Hence, it makes sense to consider minimal idempotent ideals of the left perfect ring R , i.e., ideals of R which are minimal in the set of all idemponent ideals of R .