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definability by formulas in first-order logic, e.g. as explained at https://en.wikipedia.org/wiki/Definable_set, or as in J. Robinson's first-order definition of the integers in the field of rationals

4 votes
0 answers
549 views

A question regarding the "math tea" argument

Joel David Hamkins published a paper where he analyzes the "math tea" argument, namely, the argument that some real numbers are undefinable. He constructed a countable model of set theory where all se …
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0 votes
1 answer
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An infinite Leibnizian structure in a finite language with precisely $n$ definable elements

This question was inspired by Joel David Hamkins's excellent question on Leibnizian structures with no definable elements. Let $n$ be a positive integer. Is there an infinite structure in a finite lan …
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7 votes
1 answer
450 views

Are no infinite subsets of the set of all propositional atoms definable in this structure, e...

I asked this on Math Stack Exchange, but apparently no one paid attention to it. So, I am asking it again, filling in the background necessary to understand it. Consider a countably infinite set $P$ o …
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