Betternestedset talk - Oct 2006 - a bit of theory and vocabulary

Forgot another point:

What is exactly to be named a tree ?

I propose that in nested set, a tree is a group of records that all 
together constitute a continuous serial with their left and right 
numbers, ranging from 1 to 2*(count(records)).

WIth this definition, each scope defines a new tree, while virtual 
roots can be member of the same tree.