[FOM] Interpretability in Q

[Edward T. Dean]

I have been skimming through Edward Nelson's _Predicative Arithmetic_ recently, and he writes (at the tail end of Ch. 15) that he does not know the answer to a certain compatibility problem regarding interpretability in Robinson arithmetic: for formulas A and B, if both Q[A] and Q[B] are interpretable in Q, then is Q[A,B] interpretable in Q?  I'm just wondering if anyone on FOM does know the answer, as the book is decently aged.

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Edward T. Dean
edean at post.harvard.edu
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