Now, consider a small interval around x = 0 ; i.e., x ∈ ∈ [ − − ε ε , ε ε ] . Take a new (deformed) wave function ψ ' (x) to be defined as ψ ψ ′ ( x ) = ψ ψ ( x ) , for x < − − ε ε ; and ψ ψ ′ ( x ) = − − ψ ψ ( x ) , for x > ε ε ; and constant for x ∈ ∈ [ − − ε ε , ε ε ] . If ε ε is small enough, this is always possible to do, so that ψ ' (x) is continuous.