Suppose that the metric $g$ and field $v$ described above are such that for any $(x,P)\in{\cal M}$ there exists $C>0$ such that

where $n_{P}$ is the normal unit vector to $P$ directed inside and $\nabla_{v_{(x,P)}}\,g$ is the covariant derivative of the metric $g$ considered as a symmetric tensor on the cotangent bundle.

Then the Assumption A2 is satisfied.