Chang's conjecture

Mathematical conjecture

In model theory, a branch of mathematical logic, Chang's conjecture, attributed to Chen Chung Chang by Vaught, states that every model of type (ω2,ω1) for a countable language has an elementary submodel of type. A model is of type (α,β) if it is of cardinality α and a unary relation is represented by a subset of cardinality β. The usual notation is .

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