## Four problems concerning recursively saturated models of arithmetic.(English)Zbl 0848.03016

The paper presents four open problems. One concerns a possible converse to Tarski’s undefinability of truth theorem, and is of general character. The other three are more specific. The questions are about some special $$\omega_1$$-like models, initial segments of countable recursively saturated models of PA, and about extendability of automorphisms. In each case a partial answer is given. All partial solutions are based on applications of inductive satisfaction classes.

### MSC:

 03C62 Models of arithmetic and set theory 03C50 Models with special properties (saturated, rigid, etc.)
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### References:

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