It has been stated that the general proper Lorentz transformation is a product of a boost and rotation. At the infinitesimal level the product Λ Λ = ( I − − ζ ζ ⋅ ⋅ K + ⋯ ⋯ ) ( I + θ θ ⋅ ⋅ J + ⋯ ⋯ ) = ( I + θ θ ⋅ ⋅ J + ⋯ ⋯ ) ( I − − ζ ζ ⋅ ⋅ K + ⋯ ⋯ ) = I − − ζ ζ ⋅ ⋅ K + θ θ ⋅ ⋅ J + ⋯ ⋯ is commutative because only linear terms are required (products like (θ · J)(ζ · K) and (ζ · K)(θ · J) count as higher order terms and are negligible). Taking the limit as before leads to the finite transformation in the form of an exponential Λ Λ ( ζ ζ , θ θ ) = e − − ζ ζ ⋅ ⋅ K + θ θ ⋅ ⋅ J .