# dot -Tpdf classes.dot > classes.pdf ; open classes.pdf
digraph G {
	graph [rankdir=BT];
	SMUserList -> "collections.UserList"
	SpatialVector -> SMUserList
	SpatialM6 -> SpatialVector
	SpatialF6 -> SpatialVector
	SpatialVelocity -> SpatialM6
	SpatialAcceleration -> SpatialM6
	SpatialMomentum -> SpatialF6
	SpatialForce -> SpatialF6
	SpatialInertia -> SMUserList
}