Ershov Hierarchy Revisited
Yang Yue
National University of Singapore, Singapore
December 15, 2016


For a natural number n, an n-recursive enumerable (n-r.e.) set can be defined as the symmetric difference of n recursively enumerable sets. In a series of ground-breaking papers around 1970, Ershov generalized this notion to transfinite levels based on Kleenes notations of ordinals. The corresponding Turing degree structures form a natural hierarchy below the halting problem, which is often referred as Ershov hierarchies. In this talk, I will give a survey on the early results by Ershov, and present the elementary differences between those degree structures, in the end I will mention some topics that we are working on.


Date and Time: Thursday, December 15, 2016 at 14:00-16:00
Place: Niavaran Bldg., Niavaran Square, Tehran, Iran
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