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From @misc{ enwiki:1089422502, author = “{Wikipedia contributors}”, title = “Constraint Handling Rules — {Wikipedia}{,} The Free Encyclopedia”, year = “2022”, url = “https://en.wikipedia.org/w/index.php?title=Constraint_Handling_Rules&oldid=1089422502”, note = “[Online; accessed 10-December-2022]” } A CHR program, sometimes called a constraint handler, is a set of rules that maintain a constraint store, a multi-set of logical formulas. Execution of rules may add or remove formulas from the store, thus changing the state of the program. The order in which rules “fire” on a given constraint store is non-deterministic,[5] according to its abstract semantics and deterministic (top-down rule application), according to its refined semantics.[6]