I've been looking into EC. There are definite similarities to what I've been 
discussing, but I haven't come across population virtualisation yet. I've also 
checked out permutation trees in the literature and they're not what I'm doing. 
So I suppose it's best to keep it nameless for now. It's not specific to integers, 
but using integers makes it handier to use. It could just as well represent the 
variation of individuals in a GP population.

-- ray