reduce_delta

Reduce a self-contracted generalised Kronecker delta symbol to a simpler expression without self-contractions, according to \begin{equation} n! \, \delta^{a_1\cdots a_n}_{b_1\cdots b_n}\, \delta^{b_1}_{a_1} \cdots \delta^{b_m}_{a_m} = \Big[\prod_{i=1}^m \big( d-(n-i) \big) \Big] \, (n-m)!\, \delta^{a_{m+1}\cdots a_n}_{b_{m+1}\cdots b_n}\, . \end{equation} Here is an example:

Note that this requires that the indices on the Kronecker delta symbol also carry an Integer property to specify their range.