Lecture 7: Recursive saturation
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چکیده
At first sight, recursive saturation may seem an ‘unhappy marriage’ between model theory and recursion theory, as some authors put it. Nevertheless, it turns out to work wonderfully well with models of arithmetic. First and most important of all, since there are only countably many recursive sets, the number of recursive types over any infinite structure M is exactly card(M). So by an elementary chain argument, every infinite structure for a recursive language has a recursively saturated elementary extension of the same cardinality. In particular, there exist countable recursively saturated models of arithmetic. Notice no countably saturated model of arithmetic is countable because any such model must code all subsets of N. In Section 7.1, we look at some connections between recursive saturation and arithmetic. In Section 7.2, we show a general model-theoretic property possessed by all countable recursively saturated models called resplendency. The two sections are independent of each other.
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تاریخ انتشار 2015