Seminar series
Date
Wed, 13 Nov 2013
16:00
16:00
Location
C4
Speaker
Adam Ostaszewski
Organisation
LSE
Berz used the Hahn-Banach Theorem over Q to prove that the graph of a measurable subadditive function that is non-negatively Q-homogeneous consists of two lines through the origin. I will give a proof using the density topology and Steinhaus’ Sum-set Theorem. This dualizes to a much simpler category version: a `Baire-Berz Theorem’. I will give the broader picture of this using F. Burton Jones’ analysis of additivity versus linearity. Shift-compactness and special subsets of R will be an inevitable ingredient. The talk draws on recent work with Nick Bingham and separately with Harry I. Miller.