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Let R be a ring with an endomorphism σ and F ∪ {0} the free monoid generated by U = {u 1, ..., ut } with 0 added, and M = F ∪ {0}/(I) where I is the set of certain monomial in U such that M n = 0, for some n. Then we can form the non-semiprime skew monoid ring R[M; σ]. An element a ∈ R is uniquely strongly clean if a has a unique expression as a = e + u, where e is an idempotent and u is a unit with ea = ae. We show that a σ-compatible ring R is uniquely clean if and only if R[M; σ] is a uniquely clean ring. If R is strongly π-regular and uniquely strongly clean, then R[M; σ] is uniquely strongly clean. It is also shown that idempotents of R[M; σ] (and hence the ring R[x; σ]=(x n )) are conjugate to idempotents of R and we apply this to show that R[M; σ] over a projective-free ring R is projective-free. It is also proved that if R is semi-abelian and σ(e) = e for each idempotent e ∈ R, then R[M; σ] is a semi-abelian ring.
It is proved that the set of all idempotent operations defined on a given set forms a Menger algebra which can be characterized by its densely embedded v-ideal. We also describe automorphisms of this algebra.
Abstract
A non-simple idempotent *-ring with zero centre is constructed and a negative answer to a question of G. Tzintzis concerning a hypoidempotent radical property is given.
Abstract
We prove that all maximal subgroups of the free idempotent generated semigroup over a band B are free for all B belonging to a band variety V if and only if V consists either of left seminormal bands, or of right seminormal bands.
Császár (1963) and Deák (1991) have introduced the notion of half-completeness in quasi-uniform spaces which generalizes the well known notion of bicompleteness. In this paper, for any quasi-uniform space, we construct a half-completion, called standard half-completion. The standard half-completion coincides with the usual uniform completion in the case of uniform spaces. It is also an idempotent operation in the sense that the standard half-completion of a half-complete quasi-uniform space coincides (up to a quasi-isomorphism) with the space itself.
Abstract
For semiprime involution rings, we determine some ∗-minimal ∗-ideals using idempotent elements. Nevertheless, ∗-minimal ∗-biideals are characterized by idempotent elements. Moreover, the involutive version of a theorem due to Steinfeld, which investigates a semiprime involution ring A if A=SocA, is given. Finally, semiprime involution rings having no proper nonzero ∗-biideals are characterized.
Abstract
Let R be an associative ring with unit and let N(R) denote the set of nilpotent elements of R. R is said to be stronglyπ-regular if for each x∈R, there exist a positive integer n and an element y∈R such that x n=x n +1 y and xy=yx. R is said to be periodic if for each x∈R there are integers m,n≥ 1 such that m≠n and x m=x n. Assume that the idempotents in R are central. It is shown in this paper that R is a strongly π-regular ring if and only if N(R) coincides with the Jacobson radical of R and R/N(R) is regular. Some similar conditions for periodic rings are also obtained.
