[FOM] Countable sets with imprediicative definitions

Margaret MacDougall Margaret.MacDougall at ed.ac.uk
Thu Nov 18 05:58:02 EST 2010

Can anyone provide examples of countable sets with impredicative 
definitions and apparently no alternative predicative definitions? Just 
to clarify, my intended notion of countable in relation to a set refers 
to the existence of a surjection from the natural numbers (or from the 
natural numbers excluding zero) to that set.

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