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math.LO2026
The theory of the Ziegler degrees
Rodney G. Downey, Steffen Lempp, Isabella Scott
The Ziegler degrees were introduced to characterize definability in group theory. In [JLSta], the authors show that the first order-theory of the Ziegler degrees (as a partial orde…
math.LO2024
Maximal towers and ultrafilter bases in computability
Steffen Lempp, Joseph S. Miller, Andre Nies +1
The tower number and the ultrafilter number are cardinal characteristics from set theory. They are based on combinatorial properties of classes of subse…