\cdbalgorithm{index\_rename}{}

Replace index names. This should preferably be avoided, but can
incidentally come in useful to relabel a large set of numbered indices
in one go, as the following example shows.
\begin{screen}{1,2}
{m#,n#}::Indices(spacetime).
A_{m1 m2 m3} B_{m4 m2};
@index_rename!(%){m}{n}{true};
A_{n1 m2 n3} B_{n4 m2};
\end{screen}
The {\tt true} argument to the algorithm indicates that numbered
indices starting with the given index name should be relabelled too.

Generically, it is a better practise to avoid renaming indices
altogether, and try to set up calculations such that they do not
depend on the names of indices.

\cdbseealgo{substitute}

