Well-Orderings
A binary relation r on a set w is called a well-ordering if it is a partial order such that every non-empty
subset has a smallest element. Because any pair has a minimum, r is actually a total order. Instead
of (c, d) ∈ r one writes c ≤ d. Actually, for well-orderings one prefers the irreflexive or strict version
of r. If r is a partial order then one has
(