We introduce a 'purely Borel' version of Gromov's notion of asymptotic dimension, and show how to use it to establish hyperfiniteness of various equivalence relations. Time permitting, we discuss hyperfiniteness of orbit equivalence relations of free actions of lamplighter groups. This is joint work with Jackson, Marks, Seward, and Tucker-Drob.
03E15 ; 28A05 ; 03E60 ; 37A15