<*mathematics*> A set with a total ordering and no infinite
descending chains. A total ordering "<=" satisfies x <= x;
x <= y <= z => x <= z; x <= y <= x => x=y; and 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.

Ordinals are isomorphism classes of well-ordered sets, just as integers are isomorphism classes of finite sets.

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