lor ′S′ = lor (A A⁻¹ SA) = (lor S)A. _i.e._, lor S behaves like a space-time vector of the first kind. If L is a multiple of the unit matrix, then by lor L will be denoted the matrix with the elements | ∂L/∂_x₁_ ∂L/∂_x₂_ ∂L/∂_x₃_ ∂L/∂_x₄_ |