Model Theory Learning Seminar

Laindon Burnett, Department of Pure Mathematics, University of Waterloo

"Honest Definitions in NIP"

We cover the idea of Honest Definitions from Pierre Simon's "A Guide to NIP Theories". In particular, we show that in an NIP theory, even if a particular type is not definable over a given set (and hence there is a bad formula which prevents it from being so), we may instead define this formula with parameters from an elementary extension, and this new defining formula is captured inside of the bad formula when we loosen ourselves and allow for object variables to come from the extension.

MC 5403