1. A method of enumerating possible complex two-dimensional graphical hierarchies for more convenience processing and/or storage, a complex two-dimensional graphical hierarchy being in the form of a tree hierarchy, the method comprising: enumerating possible tree hierarchies, in which a tree hierarchy comprises one or more signal values, configurable from a finite number (N) of nodes; determining for the enumerated tree hierarchies natural numerals associated with particular ones of the enumerated tree hierarchies, the natural numerals being based, at least in part, on a predetermined association between the tree hierarchies and the natural numerals; and storing, in a memory, the natural numerals, a natural numeral comprising one or more signal values, wherein the natural numeral comprises a product of two or more component natural numerals, the product of two or more component natural numerals comprising a subtree hierarchy among subtree hierarchies which are merged at a root node to form the associated enumerated tree hierarchy.