# Talk:Difference of Two Powers

Do we want a proof for Permutation of Indices of Summation? --Cynic-----(talk) 01:31, 24 December 2008 (UTC)

I would say so. There's a whole area of algebra involved with summations and stuff which needs a lot of work. Something else I haven't really got round to investigating how best to documenting yet. --prime mover 07:05, 24 December 2008 (UTC)

You permuted indecies twice:

- $b \circ S_n = \sum_{j=0}^{n-1} a^j \circ b^{n-j} = b^n + \sum_{j=1}^{n-1} a^{n-j} \circ b^j$
- And in the last line

We need to only do it in **ONE** place. I think it might be better to do it explicitly in the first one. Thoughts? --Cynic-----(talk) 16:45, 24 December 2008 (UTC)

Nightmare. Feel free to tidy this up, accuratise it, basically give it a good clean, I keep getting it round my neck. "Corrected" it twice already and got it wrong both times. If I do it without the summations it's trivial, of course. --prime mover 21:28, 24 December 2008 (UTC)