In the above, C is a 4×4 matrix, given in the article on the gamma matrices. Its explicit form is representation-dependent. The operator C cannot be written as a 4×4 matrix, as it is taking the complex conjugate of ψ ψ , and complex conjugation cannot be achieved with a complex 4×4 matrix. It can be written as a real 8×8 matrix, presuming one also writes ψ ψ as a purely real 8-component spinor. Letting K stand for complex conjugation, so that K ( x + i y ) = x − − i y , one can then write, for four-component spinors,