Series: Penn State Logic Seminar Date: Tuesday, November 8, 2005 Time: 2:30 - 3:45 PM Place: 106 McAllister Building Speaker: Stephen G. Simpson, Penn State, Mathematics Title: An Introduction to Degrees of Unsolvability, part 4 Abstract: In this talk I shall return to the idea of oracle programs, in order to introduce the arithmetical hierarchy over the Baire space. After that, I shall begin my discussion of basis theorems and mass problems.