For optimisation of dual evaluation, we want to sum factorise a
contraction, but know some sets of indices we just need to treat with
delta elimination. Allow caller to exclude these indices from the
factorisation routines to avoid N! behaviour for large N.
For optimisation of dual evaluation, we want to sum factorise a contraction, but know some sets of indices we just need to treat with delta elimination. Allow caller to exclude these indices from the factorisation routines to avoid N! behaviour for large N.