In the chiral representation for γ γ μ μ , the solution space is parametrised by a C 2 vector ξ ξ , with Dirac spinor solution u ( p ) = ( σ σ ⋅ ⋅ p ξ ξ σ σ ¯ ¯ ⋅ ⋅ p ξ ξ ) where σ σ μ μ = ( I 2 , σ σ i ) , σ σ ¯ ¯ μ μ = ( I 2 , − − σ σ i ) are Pauli 4-vectors and ⋅ ⋅ is the Hermitian matrix square-root.