Degrees of rigidity for Souslin trees

[bibtex key=FuchsHamkins2009:DegreesOfRigidity]

We investigate various strong notions of rigidity for Souslin trees, separating them under Diamond into a hierarchy. Applying our methods to the automorphism tower problem in group theory, we show under Diamond that there is a group whose automorphism tower is highly malleable by forcing.

Canonical seeds and Prikry trees

[bibtex key=Hamkins97:Seeds]

Applying the seed concept to Prikry tree forcing Pμ, I investigate how well Pμ preserves the maximality property of ordinary Prikry forcing and prove that Pμ Prikry sequences are maximal exactly when μ admits no non-canonical seeds via a finite iteration.  In particular, I conclude that if μ is a strongly normal supercompactness measure, then Pμ Prikry sequences are maximal, thereby proving, for a large class of measures, a conjecture of W. H. Woodin’s.