> To put it coarsely, outside ZigZag there are three different kinds of structures in computers today: linear lists (and grids i.e.~lists of lists), hierarchica

> To put it coarsely, outside ZigZag there are three different kinds of structures in computers today: linear lists (and grids i.e.~lists of lists), hierarchical trees and messes. That is really messes, not meshes. By a mess, I mean any complicated data structure, usually with one-directional links to make things even more unmanageable. That's not a mess, that's a graph.