Suppose A is an open subset of
a Carnot group G and H is another Carnot group. We show that a Lipschitz
function from A to H whose image has positive Hausdorff measure in the
appropriate dimension is bilipschitz on a subset of A of positive Hausdorff
measure. We also construct Lipschitz maps from open sets in Carnot groups to
Euclidean space that do not decrease dimension. Finally, we discuss two
counterexamples to explain why Carnot group structure is necessary for these
results.
Keywords
analysis on Carnot groups, Heisenberg groups, Grushin
plane, subriemannian, wavelets