doi          = "10.1016/S0167-6423(99)00023-4",
 doi          = "10.1017/S0956796802004409",
 doi          = "10.1145/964001.964010",
 doi          = "10.1145/224164.224223",
 doi          = "10.1145/99370.99404",
 doi          = "10.1016/0304-3975(90)90147-A",
 doi          = "10.1145/1291151.1291199",