descending
chains. A total ordering "#@=" satisfies
x #@= x
x #@= y = z = x #@= z
x #@= y = x = x = y
for all x, y: x #@= y or y #@= x
In addition, if a set W is well-ordered then all non-empty
subsets A of W have a least element, i.e. there exists x in A
such that for all y in A, x #@= y.
(1995-04-19)