@article{montague69,
  author = {Montague, J. S. and Plemmons, R. J.},
  interhash = {5c420ea16daeb1d8ac737a77bed3a51a},
  intrahash = {74a0526ce6e2a4fe8e2f0d17dc7caf5d},
  journal = {Journal of Algebra},
  pages = {575-587},
  title = {Maximal Subgroups of the Semigroup of Relations},
  volume = 13,
  year = 1969
}