Prove d⟨p⟩/dt =⟨-∂V/∂x⟩, given that d⟨p⟩/dt = -iħ∫∂/∂t (ψ*∂ψ/∂x) dx and ∂^2ψ/∂x∂t=∂^2ψ/∂t∂x Bonus points if you can tell me who's theorem this is without google.