  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.
