Automorphism groups in general
From Peano's Parlour
Revision as of 08:53, 7 February 2013 by Jschmerl (Talk | contribs) (Created page with "== Rigid models == A model M is '''rigid''' if Aut(M) is trivial -- that is, its only automorphism is the identity function. Every model of PA has a rigid elementary ...")
Rigid models
A model M is rigid if Aut(M) is trivial -- that is, its only automorphism is the identity function. Every model of PA has a rigid elementary end extension. (See [1] for a proof of this and much more.)
Question: Does every nonstandard model of PA have a rigid cofinal extension?
