Assume K is the class of models of a countable first order theory omitting countably many types. If K has a model of cardinality…
Assume K is the class of models of a countable first order theory omitting countably many types. If K has a model of cardinality \aleph_{\omega_1} does it have a model of cardinality continuum?
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Source: List of unsolved problems in mathematics (CC BY-SA 4.0)