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Sudoku/Methods/Advanced/Simultaneous Bivalue Nishio/Sudoku Addicts Workbook/150

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  • Raw puzzle.
  • SW Solver: Diabolical grade, overall score 225.
  • Stephens' estimated times: Improver: N/A, Expert: 414 mins, Genius: 138 mins.
  • Work announced 21:19
  • Files uploaded 22:25. So actual time elapsed from start of project to generation of images was 66 minutes, which included a false start, about 6 minutes lost.


Ready to run SBN[edit]

Figure 1

See Figure 1 on the right.

Because I had resolved a swordfish in the book, I did so here as well before starting coloring.

Seed 1: Contradiction[edit]

Figure 2

See Figure 2 on the left. Seed pair is r1c5={15}. The {1} chain creates {4} in two positions in c8, therefore r1c5=5.

Seed 2:[edit]

Figure 3

See Figure 3 on the right. Seed pair was r7c1={69}. With many common eliminations and confirmations, what is seen is the seed about to be confirmed as {9}, full proof of unique solution.


At no point in this process is there a "guess" as to a solution. What is done is to pick a pair for coloring, and because there may be many options, this might be considered a "guess." But it has been shown with many sudoku that the pair chosen is not critical. Rather, pairs may be more or less productive, but none are "wrong" or "errors," so this is not "trial and error." It is a systematic and fully logical examination of the consequences of two exclusive possibilities. It looks complicated, but the actual process is simple at each step. What has been missed in many descriptions of bifurcation is the interaction between the forks or "legs," as I call them.

See also[edit]