Abstract
Theorem 0.1 Let \(\mathbf {K}\) be an abstract elementary class (AEC) with amalgamation and no maximal models. Let \(\lambda > {LS}(\mathbf {K})\). If \(\mathbf {K}\) is categorical in \(\lambda \), then the model of cardinality \(\lambda \) is Galois-saturated.
This answers a question asked independently by Baldwin and Shelah. We deduce several corollaries: \(\mathbf {K}\) has a unique limit model in each cardinal below \(\lambda \), (when \(\lambda \) is big-enough) \(\mathbf {K}\) is weakly tame below \(\lambda \), and the thresholds of several existing categoricity transfers can be improved.
We also prove a downward transfer of solvability (a version of superstability introduced by Shelah):
Corollary 0.2 Let \(\mathbf {K}\) be an AEC with amalgamation and no maximal models. Let \(\lambda> \mu > {LS}(\mathbf {K})\). If \(\mathbf {K}\) is solvable in \(\lambda \), then \(\mathbf {K}\) is solvable in \(\mu \).
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Vasey, S. Saturation and solvability in abstract elementary classes with amalgamation. Arch. Math. Logic 56, 671–690 (2017). https://doi.org/10.1007/s00153-017-0561-8
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DOI: https://doi.org/10.1007/s00153-017-0561-8
Keywords
- Abstract elementary classes
- Superstability
- Saturation
- Solvability
- Categoricity
- Indiscernibles
- Order property