@article{Tarjan75,
  author    = {Robert Endre Tarjan},
  title     = {Efficiency of a Good But Not Linear Set Union Algorithm},
  journal   = {J. ACM},
  volume    = {22},
  number    = {2},
  year      = {1975},
  pages     = {215--225},
  ee        = {http://doi.acm.org/10.1145/321879.321884},
}