For every set X, the class of ordinals that inject into X is a set, and its union is the least ordinal that does *not* inject into X — the Hartogs number ℵ(X). Provides the basic existence of uncountable well-ordered sets from ZF alone (no…
For every set X, the class of ordinals that inject into X is a set, and its union is the least ordinal that does *not* inject into X — the Hartogs number ℵ(X). Provides the basic existence of uncountable well-ordered sets from ZF alone (no…