15For ψ(+ ∞ ) = ψ(0) = 0 and ψ∗(x ) = ψ(x) we have that ∫ +∞ i⟨p⟩∕ℏ = 0 ψ(x)(d∕dx)ψ(x)dx = ∫ − 0+∞(d∕dx)ψ(x)ψ(x)dx = 0 .