  The aim of this article is to prove a Lipschitz extension theorem for
partially defined Lipschitz maps to jet spaces endowed with a left-invariant
sub-Riemannian Carnot-Carath\'eodory distance. The jet spaces give a model for
a certain class of Carnot groups, including in particular all Heisenberg
groups. The proofs or our theorems are rather elementary, they are inspired by
ideas in papers of Gromov, Young, and Lang-Schlichenmaier.
