Editing Simple algebra (universal algebra)

In [[universal algebra]], an abstract algebra ''A'' is called ''simple'' [[if and only if]] it has no nontrivial [[congruence relation]]s, or equivalently, if every homomorphism with domain  ''A''  is either [[injective]] or constant.

As congruences on rings are characterized by their ideals, this notion is a straightforward generalization of the notion from ring theory: a ring is simple in the sense that it has no nontrivial ideals if and only if it is simple in the sense of universal algebra. The same remark applies with respect to groups and normal subgroups; hence the universal notion is also a generalization of a [[simple group]] (it is a matter of convention whether a one-element algebra should be or should not be considered simple, hence only in this special case the notions might not match).

A theorem by [[Roberto Magari]] in 1969 asserts that every  variety contains a simple algebra.<ref>{{cite journal|title=Simple algebras in varieties |last1=Lampe |first1=W.A. |last2=Taylor|first2= W. |journal=Algebra Universalis |volume=14 |year=1982 |issue=1 |pages=36–43 |doi=10.1007/BF02483905|s2cid=120637415 }} The original paper is  {{cite journal|last=Magari |first=R. |title=Una dimostrazione del fatto che ogni varietà ammette algebre semplici |journal=Annalli dell'Università di Ferrara, Sez. VII |volume=14 |issue=1 |pages=1–4 |year=1969 |doi=10.1007/BF02896794|s2cid=115886103 |language=italian}}</ref>

== See also ==

* [[Simple group]]
* [[Simple ring]]
* [[Central simple algebra]]

==References==
{{Reflist}}

[[Category:Algebras]]
[[Category:Ring theory]]