The forcing flexibility conjecture for automorphism-tower heights
The forcing flexibility conjecture for automorphism-tower heights
Let be the ground model. For a centreless group , let be the least ordinal such that the automorphism tower satisfies for all , and let denote the value computed in the forcing extension . Forcing flexibility conjecture. Let and be ordinals such that if , then . Then there exist a centreless group and a notion of forcing such that
This conjecture asks whether the height of an automorphism tower can be changed to any prescribed ordinal height by passing to a suitable forcing extension, subject only to the fact that a nonzero height in the ground model remains nonzero in the extension. Earlier results showed that automorphism towers of centreless groups terminate and that their heights can increase or decrease in generic extensions, but the full simultaneous realization asserted here was not known from the supplied context.
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Sources & referencesView supporting material
Primary source
Joel David Hamkins and Simon Thomas, “Changing the heights of automorphism towers”, arXiv:math/9703204 (1997).
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