... model,¹

The Harper model has been studied since 1955, in connection with the problem of two-dimensional electrons in a magnetic field.

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... bosons.²

Bosons are elementary particles with a spin or angular momentum that is a whole-integer multiple of Planck's constant. Photons and mesons are bosons.

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...fermions³

Fermions are elementary particles with a spin that is a half-integer multiple of Planck's constant. Electrons, protons, and neutrons are fermions.

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