# Yang Yue: On a Question of Cholak and Downey

Invitation to the Logic Seminar at the National University of Singapore

Date: Wednesday, 17 September 2014, 17:00 hrs

Room: S17#04-04, Department of Mathematics, NUS

Speaker: Yang Yue

Title: On a Question of Cholak and Downey

URL: http://www.comp.nus.edu.sg/~fstephan/logicseminar.html

In a paper entitled “On the Cantor-Bendixon rank of recursively
enumerable sets” (JSL 1993), Cholak and Downey showed that for every
recursive ordinal alpha and every nonrecursive r.e. degree d,
there is an r.e. set of rank alpha and degree d.
They also asked if one can generalize the result to
Delta-0-2 degrees, i.e., for every recursive
ordinal alpha and every nonrecursive Delta-0-2
degree d there is a Delta-0-2 set of rank
alpha and degree d. I will show the answer is positive.

This is a joint work with Rod Downey and Guohua Wu.