where σ σ ¯ ¯ μ μ = ( I 2 − − σ σ x − − σ σ y − − σ σ z ) . These are two distinct forms of the Weyl equation; their solutions are distinct as well. It can be shown that the solutions have left-handed and right-handed helicity, and thus chirality. It is conventional to label these two distinct forms explicitly, thus: