LOGIC SEMINAR, Thursday October 2<br>
SPEAKER: Anand Pillay (UIUC)<br>
TITLE: Hyperimaginaries, canonical bases, compact groups<br>
ABSTRACT: I discuss a generalisation of "imaginary" elements in model
theory to "hyperimaginaries" (equivalence classes of type-definable
equivalence relations on possibly infinite tuples), and how they can be
dealt with within ordinary first order logic. I will mention their role in
finding canonical bases for (families) of types in simple theories. I will
also discuss how the structure theory for compact groups allows us to
eliminate "infinitary bounded hyperimaginaries" in favour of "finitary
bounded hyperimaginaries" under some general hypotheses.