On the other hand, in the interval x ∈ ∈ [ − − ε ε , ε ε ] we have V avg ε ε ′ = ∫ ∫ − − ε ε ε ε d x V ( x ) | ψ ψ ′ | 2 = ε ε 2 | c | 2 1 + 4 3 | c | 2 ε ε 3 ∫ ∫ − − ε ε ε ε d x V ( x ) ≃ ≃ 2 ε ε 3 | c | 2 V ( 0 ) + ⋯ ⋯ , which holds to order ε ε 3 .