Sion Arrowsmith <siona at chiark.greenend.org.uk> writes: > sum(sequence, start=0) -> value > > If you're using sum() as a 1-level flatten you need to give it > start=[]. Oh, right, I should have remembered that. Thanks. Figuring out whether it's quadratic or linear would still take an experiment or code inspection which I'm not up for at the moment.