A $$C^m$$ Lusin approximation theorem for horizontal curves in the Heisenberg group

We prove a $$C^m$$ Lusin approximation theorem for horizontal curves in the Heisenberg group. This states that every absolutely continuous curve whose velocity is $$m-1$$ times $$L^1$$ differentiable almost everywhere coincides with except on set of small measure. Conversely, we show result no longer holds if differentiability replaced by approximate differentiability. shows our optimal and highlights differences between Euclidean settings.