Thanks to everyone for your explanations; and sorry about the group blunder ;) of course Brent is right, I should have said "R_+^*" plus multiplication. I will keep an eye on what the Haskell people do about Hierarchies of mathematical classes. Cheers Christian On Wed, 2011-03-16 at 16:03 +0100, beginners-request@haskell.org wrote:

Re: Expressing the idea of a group in Haskell