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Walter Hower originally proposed this problem as a benchmark in the Constraints Archive. He claims it has several interesting features: it concerns higher-ary constraints (not just binary ones), it is a real-world problem, it is not too complex, and it shows that local pre-processing may have little or no effect.

Walter Hower
Revisiting Global Constraint Satisfaction
Inf. Process. Lett. 66(1), 41–48, apr 1998

W. Hower
Global Constraint Satisfaction Revisited
Technical Report TR-97-02, Department of Computer Science, University College Cork, 1997