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For questions about the surreal numbers, which are a real-closed ordered proper-class-sized field that contains both the real numbers and the ordinal numbers. Thus they contain both infinite numbers (including the ordinals, but also infinite numbers like ω-1 and sqrt(ω)) and infinitesimal numbers (like 1/ω). They can also be identified with a subclass of two-player partisan games.

43 votes
4 answers
3k views

What do we know about the computable surreal numbers?

The surreal numbers are built up in a natural iterative process, by which at any ordinal stage, if one has two sets of surreal numbers $L$ and $R$, with every number $x_L$ in $L$ strictly below every …
Joel David Hamkins's user avatar
21 votes
1 answer
855 views

Is there a minimal (least?) countably saturated real-closed field?

I heard from a reputable mathematician that ZFC proves that there is a minimal countably saturated real-closed field. I have several questions about this. Is there a soft model-theoretic construction …
Joel David Hamkins's user avatar
18 votes
0 answers
885 views

Is the universality of the surreal number line a weak global choice principle?

I'd like to consider the principle asserting that the surreal number line is universal for all class linear orders, or in other words, that every linear order (including proper-class-sized) linear ord …
Joel David Hamkins's user avatar
10 votes
0 answers
376 views

Can one define in ZFC a directed system of embeddings on the class of all linear orders real...

Consider the surreal line $\langle\newcommand\No{\text{No}}\No,\leq\rangle$, in its order structure only. This is a proper class linear order, which is universal for all set-sized linear orders, as we …
Joel David Hamkins's user avatar
17 votes
2 answers
2k views

Do the surreal numbers enjoy the transfer principle in ZFC?

The surreal field $\newcommand\No{№}\No$ is definable in ZFC, and it is easy to see that the surreal order is $\kappa$-saturated for every cardinal $\kappa$, precisely because we fill any specified ga …
Joel David Hamkins's user avatar