For a 2D system of N electrons in the presence of a perpen B field and parallel E field the resistance comes out quantized proportional to h/e. And I know this result can be obtained by finding the probablity current for the lowest Landua level wavefunction. But isn't the resistance quanitization a result of electron interaction between Landau levels? i.e. once the lowest level has 'filled up' (paulis exclusion) the electrons have to jump the E gap to the next level. So how can quanitized resistance come out of the lowest wavefunction?