Automorphisms of Countable Recursively Saturated Models of PA: A Survey
Henryk Kotlarski · Notre Dame Journal of Formal Logic · 1995
We give a survey of automorphisms of countable recursively saturated models of Peano Arithmetic.Let me begin with the pre-history of the subject.The question whether PA has a model with a nontrivial automorphism (i.e., such that its elements cannot be "individualized") was due to Hasenjäger.It was solved positively by Ehrenfeucht and Mostowski [3].Their result and the idea of indiscernibility is nowadays so well known that Hodges [5] writes "today model theorists use it at least once a week," so let me omit the statement of the Ehrenfeucht-Mostowski Theorem.Another result I would like to put to the pre-history of the subject is