“…In contrast, little work had been done on such consistencies for non-binary constraints until very recently, whereas a number of consistencies that are stronger than GAC, but not domain filtering, have been developed. For example, pairwise consistency [7], hyper-m-consistency [8], relational consistency [11], and ω-consistency [9]. However, these consistencies are rarely used in practice, mainly because they have a high space complexity.…”