This is an excellent link, thanks for that! Pettis goes over similar identities, but this is much pithier, and all in one place. (Probably: Pettis assumes his

This is an excellent link, thanks for that! Pettis goes over similar identities, but this is much pithier, and all in one place. (Probably: Pettis assumes his readership already knows these things; I'm definitely not as savvy as his intended reader I think.)