文摘
A Carnot group \(\mathbb {G}\) admits Lusin approximation for horizontal curves if for any absolutely continuous horizontal curve \(\gamma \) in \(\mathbb {G}\) and \(\varepsilon >0\), there is a \(C^1\) horizontal curve \(\Gamma \) such that \(\Gamma =\gamma \) and \(\Gamma '=\gamma '\) outside a set of measure at most \(\varepsilon \). We verify this property for free Carnot groups of step 2 and show that it is preserved by images of Lie group homomorphisms preserving the horizontal layer. Consequently, all step 2 Carnot groups admit Lusin approximation for horizontal curves.