Series: Penn State Logic Seminar Date: Tuesday, April 23, 2002 Time: 2:30 - 3:45 PM Place: 113 McAllister Building Speaker: Deirdre Haskell, Mathematics, McMaster University Title: Grothendieck Rings of Definable Sets Abstract: The collection of definable sets in a structure can be given a ring structure in a natural way. Sets are identified if there is a bijection between them whose graph is a definable set. The Grothendieck group is the free group generated by the equivalence classes, modulo the relation [X]+[Y]= [X cup Y] - [X cap Y]. The multiplication [X].[Y]= [X times Y] gives the ring structure. In this talk I will give explicit calculations of the Grothendick rings of various structures.