If the phase varies slowly as compared to the amplitude, B 0 ( x ) = 0 and A 0 ( x ) = ± ± 2 m ( V ( x ) − − E ) which corresponds to tunneling. Resolving the next order of the expansion yields Ψ Ψ ( x ) ≈ ≈ C + e + ∫ ∫ d x 2 m ℏ ℏ 2 ( V ( x ) − − E ) + C − − e − − ∫ ∫ d x 2 m ℏ ℏ 2 ( V ( x ) − − E ) 2 m ℏ ℏ 2 ( V ( x ) − − E ) 4