@InCollection{tian:pea02-r290a,
  author =       "Tian, J.\ and Pearl, J.\",
  title =        "A general identification condition for causal effects",
  booktitle =    "Proceedings of the Eighteenth National Conference on
                  Artificial Intelligence",
  publisher =    "AAAI Press/The MIT Press",
  address =      "Menlo Park, CA",
  year =         2002,
  pages =        "567--573"
}