Inner models with all reals preserve omega-one

ID: inner-models-with-all-reals-preserve-omega-one

An inner model of ZF containing all ambient subsets of computes the same countable ordinals as the ambient universe. Every ambient countably infinite ordinal has a well-order code coded by a subset of , hence that code belongs to ; finite ordinals are already shared. The Mostowski collapse theorem inside recovers the actual ordinal and its countability witness. Conversely any countability witness in remains one outside. If also contains the full power set of as a set, its Continuum hypothesis would give an ambient bijection from onto that same power set. Thus an ambient failure of this well-orderable formulation of the Continuum hypothesis is preserved in such an inner model. No internal axiom of choice is required for this argument.

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