VertexTraitsBase< T > Node1 VertexTraitsBase< T >   + x() + y() + z() + dx() + dy() + dz() + nTrackParticles() + chiSquared() + numberDoF() + time() + vertexType() Node2 VertexTraits< const T >   + x() + y() + z() + dx() + dy() + dz() + nTrackParticles() + chiSquared() + numberDoF() + time() + vertexType() Node1->Node2 Node3 VertexTraits< T >     Node1->Node3 Node3->Node2