A Banach principle for semifinite von Neumann algebras.
Let M be a finite von Neumann algebra acting on the standard Hilbert space L²(M). We look at the space of those bounded operators on L²(M) that are compact as operators from M into L²(M). The case where M is the free group factor is particularly interesting.
In this note we study sets of normal generators of finitely presented residually -finite groups. We show that if an infinite, finitely presented, residually -finite group is normally generated by with order , then where denotes the first -Betti number of . We also show that any -generated group with must have girth greater than or equal .
We introduce a property of ergodic flows, called Property B. We prove that an ergodic hyperfinite equivalence relation of type III₀ whose associated flow has this property is not of product type. A consequence is that a properly ergodic flow with Property B is not approximately transitive. We use Property B to construct a non-AT flow which-up to conjugacy-is built under a function with the dyadic odometer as base automorphism.