where ∇ ∇ ρ ρ ( k ) ϕ ϕ = ′ ∇ ∇ ρ ρ 1 . . . ∇ ∇ ρ ρ k ϕ ϕ + symmetrization − − traces ′ are symmetrized derivatives with traces subtracted. The most important information is in the coefficients ξ ξ k , η η k , ζ ζ k and in the prefactor R e ( b 1 2 ) , where b 1 = exp ⁡ ⁡ [ i θ θ ] is a free parameter that the equations have, see Other dimensions, extensions, and generalisations. It is important to note that the usual stress-tensor has no more than two derivative and the terms k > 0 are not independent (for example, they contribute to the same ⟨ ⟨ T a b j 0 j 0 ⟩ ⟩ AdS/CFT three-point function). This is a general property of field theories that one can perform nonlinear (and also higher derivative) field redefinitions and therefore there exist infinitely many ways to write the same interaction vertex at the classical level. The canonical stress-tensor has two derivatives and the terms with contracted derivatives can be related to it via such redefinitions.