# rename_dummies

Rename dummy indices.

Rename the dummy indices in an expression. This can be necessary in
order to make various terms in a sum use the same names for the
indices, so that they can be collected.{m,n,p,q,r,s}::Indices(vector);
ex:=A_{m n} B_{m n} - A_{p q} B_{p q};

\(\displaystyle{}\text{Attached property Indices(position=free) to }\left(m, \mmlToken{mo}[linebreak="goodbreak"]{} n, \mmlToken{mo}[linebreak="goodbreak"]{} p, \mmlToken{mo}[linebreak="goodbreak"]{} q, \mmlToken{mo}[linebreak="goodbreak"]{} r, \mmlToken{mo}[linebreak="goodbreak"]{} s\right).\)

\(\displaystyle{}A_{m n} B_{m n}-A_{p q} B_{p q}\)

Using

`canonicalise`

does nothing here, canonicalise(_);

\(\displaystyle{}A_{m n} B_{m n}-A_{p q} B_{p q}\)

However, renaming indices does the trick,

rename_dummies(_);

\(\displaystyle{}0\)

Note that the indices need to have been declared as being part of an
index list, using the

`Indices`

property.