Christian Bessière Emmanuel Hebrard Brahim Hnich Zeynep Kiziltan Toby Walsh The Range and Roots Constraints: Specifying Counting and Occurrence Problems. 60-65 2005 conf/ijcai/2005 IJCAI http://www.ijcai.org/papers/0735.pdf db/conf/ijcai/ijcai2005.html#BessiereHHKW05