[FOM] Countable sets with imprediicative definitions
friedman at math.ohio-state.edu
Thu Nov 18 11:20:28 EST 2010
On Nov 18, 2010, at 5:58 AM, Margaret MacDougall wrote:
> Can anyone provide examples of countable sets with impredicative
> definitions and apparently no alternative predicative definitions?
> to clarify, my intended notion of countable in relation to a set
> to the existence of a surjection from the natural numbers (or from the
> natural numbers excluding zero) to that set.
Is this the kind of thing you are looking for?
The set of all finitely presented structures with domain N, in a
finite relational type, all of whose substructures are finitely
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