We introduce novel equations, in the spirit of rough path theory, that parametrize level sets of intrinsically regular maps on the Heisenberg group with values in R2. These equations can be seen as a sub-Riemannian counterpart to classical ODEs arising from the implicit function theorem. We show that they enjoy all the natural well-posedness properties, thus allowing for a ‘good calculus’ on nonsmooth level sets. We apply these results to prove an area formula for the intrinsic measure of level sets, along with the corresponding coarea formula.
Magnani, V., Stepanov, E., & Trevisan, D. (2018). A rough calculus approach to level sets in the Heisenberg group. Journal of the London Mathematical Society, 97(3), 495–522. https://doi.org/10.1112/jlms.12115