Series: Penn State Logic Seminar Date: Tuesday, March 29, 2005 Time: 2:30 - 3:45 PM Place: 103 Pond Laboratory Speaker: John Clemens, Penn State, Mathematics Title: Potential Borel Sets and Stern Absoluteness Abstract: Stern absoluteness is a principle which says, in effect, that Borel sets which can be added by Cohen's method of forcing can be added by small forcings. Using this principle, one can prove many absolute theorems about the Borel hierarchy. I will give an overview of this technique and present several applications, including a proof of Friedman's theorem about Borel diagonalizers.