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The problem of two-dimensional localization in the presence of a magnetic field is reconsidered. The existence of extended electronic states is demonstrated by use of the replica formalism and duality arguments. These states are analogs of = vacua in four-dimensional Yang-Mills theories, and occur at the center of each Landau band. The present results complete the explanation of the integrally quantized Hall effect.
Levine et al. (Mon,) studied this question.