Reasonable non--Radon--Nikodym ideals
arXiv:0806.4760 · doi:10.1016/j.topol.2008.11.008
Abstract
For any abelian Polish sigma-compact group H there exist a sigma-ideal Z over N and a Borel Z-approximate homomorphism f : H --> H^N which is not Z-approximable by a continuous true homomorphism g : H --> H^N.