Degrees of rigidity for Souslin trees
  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. 
Joel David Hamkins (The City University of New York) and Gunter Fuchs   (Westf\"alische Wilhelms-Universit\"at M\"unster)