Dirac Hamiltonian symmetry group

The purpose of these two sections has been to provide an easy introduction to the subject of double groups. We now turn to a more formal treatment of the symmetry of the Dirac Hamiltonian. However, the material covered above should provide sufficient background to follow our subsequent discussion of the use of symmetry in applications and implementations of the methods, and the reader mainly oriented toward these aspects may get by with skimming the remainder of this chapter at a first reading. 

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