Alan M. Frisch Matthew Grum Christopher Jefferson Bernadette Martínez Hernández Ian Miguel The Design of ESSENCE: A Constraint Language for Specifying Combinatorial Problems. 80-87 2007 conf/ijcai/2007 IJCAI http://dli.iiit.ac.in/ijcai/IJCAI-2007/PDF/IJCAI07-011.pdf db/conf/ijcai/ijcai2007.html#FrischGJHM07