0.1
Cardinality
N = = 0 =the natural numbers= cfw_0, 1, 2, 3, . . .
We usually identify a natural number with the set of its predecessors: n = cfw_0, 1, 2, . . . , n 1 In particular, 0 = .
Denition 0.1. A is equinumerous with B provided there is a biject
Ordinals - summary
Here is everything you really need to know about ordinals:
1. The denition: An ordinal number is a set such that (i) the
elements of are well-ordered (by ), and (ii) (transitivity) If
x y then x
2. It follows that every element of an o