The standard model of Peano Arithmetic is pointwise definable, because every finite natural number is parameter-free definable. What about the converse? That is, if a model $M$ of PA is pointwise definable, must it be the standard model? Also, bonus question, are there even nonstandard models of PA which are pointwise definable, and some that are not?
2026-03-27 10:39:49.1774607989
Is pointwise definability of a model of PA equivalent to it being the standard model?
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