Flexible identity

A condition on a binary operation $\cdot$ on a set $X$: that for all $x, y \in X$ $$x \cdot (y \cdot x) = (x \cdot y) \cdot x \ .$$

In the context of non-associative rings and algebras, a flexible ring or algebra is one whose multiplication satisfies the flexible identity, which may be expressed in terms of the vanishing of the associator $(x,y,x)$.