### The lengths of Pi11 ranks

Logic and Set Theory Seminar

26th February 2020, 3:00 pm – 4:00 pm

Fry Building, G.07

A rank stratifies a set of reals as a union of simpler sets. Natural examples come from ranks of trees and halting times of infinite time Turing machines with real inputs. In joint work with Merlin Carl and Philip Welch, we prove several results towards the general goal of characterizing the existence of ranks of a given complexity and prescribed countable length on a set.

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