and was the first equation to accurately predict spin, a consequence of the 4 × 4 gamma matrices γ = β, γ = (γ 1, γ 2, γ 3) = β α = (βα 1, βα 2, βα 3). There is a 4 × 4 identity matrix pre-multiplying the energy operator (including the potential energy term), conventionally not written for simplicity and clarity (i.e. treated like the number 1). Here ψ is a four-component spinor field, which is conventionally split into two two-component spinors in the form: