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      "statement": "# Knuth: reversible list operations for exact-cover search\n\nKnuth presented dancing links as an implementation technique for backtracking, using reversible deletion and restoration of nodes in doubly linked lists and applying it to Algorithm X for exact cover.\n\nDuring a tentative choice, incompatible rows and columns can be removed and then restored cheaply when the search backtracks. The data structure makes changing constraints manageable while leaving the underlying combinatorial search problem intact.\n\n## Scientific scope\n\nThis is a search implementation technique, not a polynomial-time algorithm for general exact cover. The opening credits Hitotumatu and Noshita's earlier use of reversible list operations.\n\n## People and systems\n\nDonald E. Knuth\n\n\n\n## Original sources\n\n- [Dancing Links (2000)](https://arxiv.org/abs/cs/0011047)\n",
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