Ranked lattices and elementary end extensions
The City University of New York
Every countable model M of PA has and elementary end extension N such that the lattice Lt(N/M) is
isomorphic to the pentagon lattice N_5. I will go over the proof why none of such extensions can be conservative.
Roman Kossak is professor of mathematics at The City University of New York, at Bronx Community College and also at the CUNY Graduate Center. He conducts research in mathematical logic, especially in model theory of Peano Arithmetic.