In the last ten years the problem has forsaken its underground existence by appearing in various forms as a problem in books and journals, sometimes without attribution as an unsolved problem. Prizes have been offered for its solution: $50 by H. S. M. Coxeter in 1970, then $500 by Paul Erdös, and more recently 1000 by B. Thwaites [72]. Over twenty research articles have appeared on the problem and related problems.
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