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Abstract The relativistic wave equations currently used in physical theory are symmetrical between positive and negative energies. A new relativistic wave equation for particles of non-zero rest-mass is here proposed, allowing only positive values for the energy. There is great formal similarity between it and the usual relativistic wave equation for the electron, but the physical significance is very different. In particular, the new equation gives integral values for the spin.
P. A. M. Dirac (Tue,) studied this question.