Tag Archives: Sudoku multiple solutions

How Not to Find a Multiple on Moito’s Road


After a jaw dropping irregular XYZ-wing, a marking mistake reveals an unavoidable UR and two solutions of Very Hard IV-6, then the correction leads to an even more remarkable, but no less unavoidable uniqueness violation. Coloring reveals the logical path … Continue reading

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Slink vs. Coloring Networks and Illogical Sudoku


This post reports a surprising fact about multiple solution puzzles, that solutions found by backtracking tree search can be logically inconsistent. Specifically, such solutions violate the coloring network implied by the givens. I happened on this fact by means of … Continue reading

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Another Look at Ardson Very Hard v.2 38


This post brings up an interesting question about the multiple solution puzzle: Does its ambiguity prevent strictly logical solving from reaching a solution? Introducing the first selected review puzzle of the A.D. Ardson Very Hard v.2 collection on April 11, … Continue reading

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THLS vs. Unique Rectangle


This post updates the UR chart, with credit to Denis Berthier, then debunks another unfortunate THLS pronouncement. The homework puzzle illustrates another penalty a human solver pays for interpreting  The Hidden Logic of Sudoku as solving advice. Now in our … Continue reading

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The Fiendish 100 BUG-gy Maze


Bad news for Su Doku Master Wayne Gould. Fiendish 100, the only “Fiendish” of our Train Your Brain Su Doku Fiendish review to survive line marking, is found to have at least 15 solutions. The solutions are revealed in multiple … Continue reading

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