## lower_free_indices

Make all free indices in an expression subscripts.

Free indicies (indices declared with the `Indices(position=free)`

property) can appear as subscripts or superscripts,
but sometimes it is useful to move them all into the same position. {a,b,c}::Indices(name=A, position=free);
{m,n,p}::Indices(name=B, position=fixed);
ex:=A_{a b m} B^{a b m};

\(\displaystyle{}\text{Attached property Indices(position=free) to }\left[a, b, c\right].\)

\(\displaystyle{}\text{Attached property Indices(position=fixed) to }\left[m, n, p\right].\)

\(\displaystyle{}A_{a b m} B^{a b m}\)

A_{a b m} B^{a b m}

lower_free_indices(_);

\(\displaystyle{}A_{a b m} B_{a b}\,^{m}\)

A_{a b m} B_{a b}^{m}

The opposite of this is

`raise_free_indices`

, which moves all indices to be superscripts.