Invitation to the Logic Seminar at the National University of Singapore
Date: Friday, 4 November 2016, 13:00 hrs and 14:00 hrs
Room: S17#07-24, Department of Mathematics, NUS
Talk 1 – Speaker: Liu Yong.
Title: Revisit maximal d.r.e. degrees.
Abstract: We will begin with a brief review of maximal d.r.e. construction,
and show that for any cappable r.e. set A, there is a maximal d.r.e. set D,
which computes A. We also show how to build a maximal d.r.e. set D, avoiding
upper cone of two nonrecursive r.e. sets.
Talk 2 – Speaker: Peng Cheng
Title: A brief introduction to the Ershov hierarchy.
Abstract: Ershov generalized the n-r.e. hierarchy to transfinite levels
based on Kleene’s ordinals. It is a natural measure to study the sets below K.
We will survey some early work by Ershov and others on the Ershov hierarchy
and present the most fundamental results. We will also provide some questions
we are thinking now.