von Neumann ordinal


von Neumann ordinal

(mathematics)An implementation of ordinals in set theory(e.g. Zermelo Fr?nkel set theory or ZFC). The von Neumannordinal alpha is the well-ordered set containing just theordinals "shorter" than alpha.

"Reasonable" set theories (like ZF) include Mostowski'sCollapsing Theorem: any well-ordered set is isomorphic toa von Neumann ordinal. In really screwy theories (e.g. NFU --New Foundations with Urelemente) this theorem is false.

The finite von Neumann ordinals are the von Neumann integers.