Abstract
For a natural number n, an nrecursive enumerable (nr.e.) set can be defined as the symmetric difference of n recursively enumerable sets. In a series of groundbreaking 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.
Information:
Date and Time:  Thursday, December 15, 2016 at 14:0016:00

Place:  Niavaran Bldg., Niavaran Square, Tehran, Iran 
