1 | initial version |

There seems to be room for improvement in the design here. Basis elements apparently have the same parent as ordinary elements, and `a.monomials()`

returns them as such, which makes it hard to get at the underlying tree.

From the source code, accessed by `a??`

, we find that we can access the actual monomial by e.g.:

```
sage: a_tree = a.list()[0][0]; a_tree
[[x0, x1], x1]
sage: isinstance(a_tree, sage.algebras.lie_algebras.lie_algebra_element.LyndonBracket)
True
sage: a_tree._left
[x0, x1]
sage: a_tree._right
x1
```

You may want to discuss this on sage-devel.

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