The zilch is often described in terms of the zilch tensor, Z ν ν ρ ρ μ μ . The latter can be expressed using the dual electromagnetic tensor F ^ ^ μ μ ν ν = ( 1 / 2 ) ϵ ϵ μ μ ν ν ρ ρ σ σ F ρ ρ σ σ as Z ν ν ρ ρ μ μ = F ^ ^ μ μ λ λ F λ λ ν ν , ρ ρ − − F μ μ λ λ F ^ ^ λ λ ν ν , ρ ρ .