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Model theory is the branch of mathematical logic which deals with the connection between a formal language and its interpretations, or models.

9 votes
2 answers
639 views

A "surnatural numbers" as a largest model of the natural numbers

One characteristic of the surreal numbers is that they are a monster model of the first-order theory of real numbers, according to Joel David Hamkins in this post. Thus they are real-closed, and every …
Mike Battaglia's user avatar
5 votes
0 answers
231 views

Surreal numbers and the ultrafilter lemma

In this question, I asked how to interpret a historical claim made by Conway regarding the potential, if not ideal, use of the surreal numbers for nonstandard analysis. In the comments and answers it …
Mike Battaglia's user avatar
9 votes
1 answer
307 views

Transfinitely iterating the Levi-Civita, Hahn or Puiseux constructions

This question was originally asked at MSE but seems too advanced, so I'm reposting it here. In short, the idea is that many constructions for non-Archimedean fields can naturally be iterated, in some …
Mike Battaglia's user avatar
27 votes
1 answer
2k views

Are Conway's combinatorial games the "monster model" of any familiar theory?

This is related to this question about a "mother of all" groups, and so seemed like it'd fit in better at MO than MSE. If I understand the answer to that question correctly, the surreal numbers have …
Mike Battaglia's user avatar
5 votes
1 answer
577 views

The "first-order theory of the second-order theory of $\mathrm{ZFC}$"

$\newcommand\ZFC{\mathrm{ZFC}}\DeclareMathOperator\Con{Con}$It is often interesting to look at the theory of all first-order statements that are true in some second-order theory, giving us things like …
Mike Battaglia's user avatar
27 votes
4 answers
3k views

What "metatheory" did early set theory/logic researchers use to prove semantic results?

Things like the first-order completeness theorem and the Löwenheim-Skolem theorem are considered foundational in mathematical logic. The modern approach seems to be, usually, to interpret a "model" s …
Mike Battaglia's user avatar