Abstract
We investigate various strong notions of rigidity for Souslin trees, separating them under ♢ into a hierarchy. Applying our methods to the automorphism tower problem in group theory, we show under ♢ that there is a group whose automorphism tower is highly malleable by forcing.
Gunter Fuchs. Joel David Hamkins. "Degrees of rigidity for Souslin trees." J. Symbolic Logic 74 (2) 423 - 454, June 2009. https://doi.org/10.2178/jsl/1243948321
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