Engel identity

The Engel identity, named after Friedrich Engel, is a mathematical equation that is satisfied by all elements of a Lie ring, in the case of an Engel Lie ring, or by all the elements of a group, in the case of an Engel group. The Engel identity is the defining condition of an Engel group.

A Lie ring ${\displaystyle L}$ is defined as a nonassociative ring with multiplication that is anticommutative and satisfies the Jacobi identity with respect to the Lie bracket ${\displaystyle [x,y]}$, defined for all elements ${\displaystyle x,y}$ in the ring ${\displaystyle L}$. The Lie ring ${\displaystyle L}$ is defined to be an n-Engel Lie ring if and only if

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