Decimal Numbering Rule
l
The successor of x0 (concatenation)
is x1, the successor of x1 is x2, É,
and the successor of x8 is x9.
l
The successor of x9 is y0 where y is
the successor of x.
l
Example: 0, 1, É, 9, 10, 11, É, 19, 20,
21, É, 99, 100, ...