sequence multiplied by -1

[Lawrence D'Oliveiro]

In message <slrni9u4kv.28r0.usenet-nospam at guild.seebs.net>, Seebs wrote:

> Helps, perhaps, that I got exposed to group theory early enough to be used
> to redefining + and * to be any two operations which have interesting
> properties ...

But groups only have one such operation; it’s rings and fields (and number 
systems) that have two.