Stationarity dichotomy conjecture for abstract elementary classes

About 13 years old · traced to

Let k{\mathfrak k} be an abstract elementary class and define

Cℵ0fp={λ:λ=ℶλ and cf(λ)=ℵ0}.C^{\rm fp}_{\aleph_0}=\{\lambda:\lambda=\beth_\lambda\text{ and }{\rm cf}(\lambda)=\aleph_0\}.

Set

S1={λ∈Cℵ0fp:I˙(λ,k)<λ},S2={λ∈Cℵ0fp:I˙(λ,k)≥λ}.S_1=\{\lambda\in C^{\rm fp}_{\aleph_0}:\dot I(\lambda,\mathfrak k)<\lambda\},\qquad S_2=\{\lambda\in C^{\rm fp}_{\aleph_0}:\dot I(\lambda,\mathfrak k)\geq\lambda\}.

Stationarity dichotomy conjecture. The classes S1S_1 and S2S_2 are not both stationary. A weaker version replaces S2S_2 by the class of λ∈Cℵ0fp\lambda\in C^{\rm fp}_{\aleph_0} such that every M∈KλkM\in K^{\mathfrak k}_\lambda has ≤k\leq_{\mathfrak k}-extensions of every cardinality greater than λ\lambda. The source presents these as conjectures motivated by controlling the categoricity spectrum, with no resolution stated.

References

Primary source

Saharon Shelah, “A.E.C. with not too many models”, arXiv:1302.4841 (2013).

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