However, the contribution to the potential energy from this region for the state ψ with a node is V avg ε ε = ∫ ∫ − − ε ε ε ε d x V ( x ) | ψ ψ | 2 = | c | 2 ∫ ∫ − − ε ε ε ε d x x 2 V ( x ) ≃ ≃ 2 3 ε ε 3 | c | 2 V ( 0 ) + ⋯ ⋯ , lower, but still of the same lower order O ( ε ε 3 ) as for the deformed state ψ ', and subdominant to the lowering of the average kinetic energy. Therefore, the potential energy is unchanged up to order ε ε 2 , if we deform the state ψ ψ with a node into a state ψ ' without a node, and the change can be ignored.