
 Ordinal number (Site not responding. Last check: 20071022) 
  Category:Set theory Ordinal numbers, or ordinals for short, are numbers used to denote the position in an ordered sequence: first, second, third, fourth, etc. (See How to name numbers.) In mathematics, ordinal numbers are an extension of the natural numbers to accommodate infinite sequences, introduced by Georg Cantor in 1897. 
  Arithmetic operations on ordinals can be captured by algorithms that transform Cantor normal forms, similar to, but more complicated than, the algorithms for integer arithmetic in terms of the decimal notation usually taught in primary education. 
  Ordinals which don't have an immediate predecessor can always be written as a limit of a net of other ordinals (but not necessarily as the limit of a sequence, i.e. 
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