Density not realizable as the Jacobian determinant of a bilipschitz map
  Are every two separated nets in the plane bilipschitz equivalent? In the late 1990s, Burago and Kleiner and, independently, McMullen resolved this beautiful question negatively. Both solutions are based on a construction of a density function that is not realizable as the Jacobian determinant of a bilipschitz map. McMullen's construction is simpler than the Burago-Kleiner one, and we provide a full proof of its nonrealizability, which has not been available in the literature. 
Vojt\v{e}ch Kalu\v{z}a
math.MG cs.CG math.FA