The most useful relativistic quantum mechanics one-particle theories (there are no fully consistent such theories) are the Klein–Gordon equation and the Dirac equation in their original setting. They are relativistically invariant and their solutions transform under the Lorentz group as Lorentz scalars ((m, n) = (0, 0)) and bispinors ((0, ⁠ 1 / 2 ⁠) ⊕ (⁠ 1 / 2 ⁠, 0)) respectively. The electromagnetic field is a relativistic wave function according to this definition, transforming under (1, 0) ⊕ (0, 1).