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#### Open Access in DiVA

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#### Authority records

Nystedt, Patrik
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Division of Natural Sciences and Electrical and Surveying Engineering
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Journal of Algebra
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Algebra and Logic
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Simple rings and degree mapsPrimeFaces.cw("AccordionPanel","widget_formSmash_some",{id:"formSmash:some",widgetVar:"widget_formSmash_some",multiple:true}); PrimeFaces.cw("AccordionPanel","widget_formSmash_all",{id:"formSmash:all",widgetVar:"widget_formSmash_all",multiple:true});
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2014 (English)In: Journal of Algebra, ISSN 0021-8693, E-ISSN 1090-266X, Vol. 401, p. 201-219Article in journal (Refereed) Published
##### Abstract [en]

##### Place, publisher, year, edition, pages

2014. Vol. 401, p. 201-219
##### Keywords [en]

Degree map, Ideal associativity, Ring extension, Simplicity
##### National Category

Algebra and Logic
##### Research subject

ENGINEERING, Mathematics
##### Identifiers

URN: urn:nbn:se:hv:diva-5902DOI: 10.1016/j.jalgebra.2013.11.023ISI: 000330599500011Scopus ID: 2-s2.0-84891812645OAI: oai:DiVA.org:hv-5902DiVA, id: diva2:692909
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PrimeFaces.cw("AccordionPanel","widget_formSmash_j_idt609",{id:"formSmash:j_idt609",widgetVar:"widget_formSmash_j_idt609",multiple:true}); Available from: 2014-02-03 Created: 2014-02-03 Last updated: 2019-11-29Bibliographically approved

For an extension A/B of neither necessarily associative nor necessarily unital rings, we investigate the connection between simplicity of A with a property that we call A-simplicity of B. By this we mean that there is no non-trivial ideal I of B being A-invariant, that is satisfying A I ⊆ I A. We show that A-simplicity of B is a necessary condition for simplicity of A for a large class of ring extensions when B is a direct summand of A. To obtain sufficient conditions for simplicity of A, we introduce the concept of a degree map for A/B. By this we mean a map d from A to the set of non-negative integers satisfying the following two conditions: (d1) if a ∈ A, then d(a) = 0 if and only if a = 0; (d2) there is a subset X of B generating B as a ring such that for each non-zero ideal I of A and each non-zero a ∈ I there is a non-zero a ' ∈ I with d(a ') ≤ d(a) and d(a 'b - ba ') < d(a) for all b ∈ X. We show that if the centralizer C of B in A is an A-simple ring, every intersection of C with an ideal of A is A-invariant, A C A = A and there is a degree map for A/B, then A is simple. We apply these results to various types of graded and filtered rings, such as skew group rings, Ore extensions and Cayley-Dickson doublings. © 2013 Elsevier Inc.

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