@article{schein70,
  author = {Plemmons, R. J. and Schein, B. M.},
  interhash = {341ee2f65ff1940a18d395f2cf5eadd4},
  intrahash = {100395cf400ac7fa3109ce84ae9bcdb8},
  journal = {Semigroup Forum},
  pages = {267-271},
  title = {Groups of Binary Relations},
  volume = 1,
  year = 1970
}