Radon-Nikodym property and area formula for Banach homogeneous group   targets
  We prove a Rademacher-type theorem for Lipschitz mappings from a subset of a Carnot group to a Banach homogeneous group, equipped with a suitably weakened Radon-Nikodym property. We provide a metric area formula that applies to these mappings and more generally to all almost everywhere metrically differentiable Lipschitz mappings defined on a Carnot group. 
Valentino Magnani and Tapio Rajala
math.FA math.MG