Description: The class of all cardinal numbers is not a set (i.e. is a proper class).
Theorem 19.8 of Eisenberg p. 310. In this proof (which does not use
AC), we cannot use Cantor's construction canth3 to ensure that there
is always a cardinal larger than a given cardinal, but we can use
Hartogs' construction hartogs to construct (effectively)
( alephsuc A ) from ( alephA ) , which achieves the same
thing. (Contributed by Mario Carneiro, 22-Jan-2013)