The components of the resulting spin vector, j → → , always satisfy S U ( 2 ) commutation relations, but the individual components will depend on the choice of boost Λ Λ − − 1 ( P ) μ μ ν ν . The light-front components of the spin are obtained by choosing Λ Λ − − 1 ( P ) k μ μ to be the inverse of the light-front preserving boost, (4).