Full Idea
For a set to be 'well-ordered' it is required that every subset of the set has a first element.
Gist of Idea
A set is 'well-ordered' if every subset has a first element
Source
Brian Clegg (Infinity: Quest to Think the Unthinkable [2003], Ch.13)
Book Reference
Clegg,Brian: 'Infinity' [Robinson 2003], p.168