in deriving quantization of flux in superconductor ring, the momentum of cooper pair p: [tex]p=\hbar\nabla\theta=e^*(\Lambda J_s + A)[/tex] then integrate around the ring, [tex]\hbar\oint\nabla\theta dl=e^*\oint(\Lambda J_s + A)dl[/tex] using stoke's theorem and integrate sufficiently deep in the ring where current density is very small, the RHS becomes [tex]RHS=e^*\Phi_s[/tex] and the left hand side,becomes hn where n is integer. So the quantized flux is [tex]\Phi_s=nh/e^*[/tex] e star is the effective cooper pair charge which is -2e. i got confused here,why the left hand side integral becomes hn? The argument used by the book (Van Duzer, superconductivity page 116) is that because theta is unique or differ by a multiple of 2 Pi at each point, so the integral [tex]\oint\nabla\theta dl=2\pi n[/tex] why?? where does n come from? theta is a scalar function of r. please help. thanks.