A ring $R$ is called von Neumann regular if for every $a \in R$; $a=axa$ for some $x \in R$.
A ring $R$ called Abelian if every idempotent in $R$ is central.
Are von Neumann regular rings abelian?
A ring $R$ is called von Neumann regular if for every $a \in R$; $a=axa$ for some $x \in R$.
A ring $R$ called Abelian if every idempotent in $R$ is central.
Are von Neumann regular rings abelian?
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$M_2(F)$ is von Neumann regular (for any field $F$), but has the noncentral idempotent $\begin{bmatrix}1&0\\0&0\end{bmatrix}$.
In fact it is known that a von Neumann regular ring is abelian if and only if it is strongly regular, meaning that for every $a\in R$ there exists a $b\in R$ such that $a^2b=a$. Strongly regular rings do not have nonzero nilpotent elements, so you can see why the matrix ring example suggests itself as a counterexample.