The solutions of the right- and left-handed Weyl equations are different: they have right- and left-handed helicity, and thus chirality, respectively. It is convenient to indicate this explicitly, as follows: σ σ μ μ ∂ ∂ μ μ ψ ψ R = 0 and σ σ ¯ ¯ μ μ ∂ ∂ μ μ ψ ψ L = 0 .