@article{10581,
  author = {W. Harter and N. dos Santos},
  title = {Double-group theory on the half-shell and the two-level system. I. Rotation and half-integral spin states},
  year = {1978},
  journal = {American Journal of Physics},
  volume = {46},
  pages = {251},
  month = {Jan-01-1978},
  issn = {00029505},
  url = {http://link.aip.org/link/?AJP/46/251/1\&Agg=doi},
  doi = {10.1119/1.11134},
}