**Flagged Revisions installed. Unapproved pages display a Red unchecked notice under the title.** Trolls attack here by creating and archiving pages with offensive content. To verify an archived page, check the original URL. Questions about administration? Contact User talk:Abd.
**Limited privacy on this site, see CFC:Limited privacy**

# Difference between revisions of "Sudoku/Methods/Advanced/Simultaneous Bivalue Nishio/Sudoku Addicts Workbook/149"

[checked revision] | [checked revision] |

(→Introduction) |
|||

Line 2: | Line 2: | ||

*[http://www.sudokuwiki.org/sudoku.htm?bd=004002005060009700000800030100000900000307000002000004080006000005100020300400600 Raw puzzle]. | *[http://www.sudokuwiki.org/sudoku.htm?bd=004002005060009700000800030100000900000307000002000004080006000005100020300400600 Raw puzzle]. | ||

*SW Solver: Extreme grade, overall score 842. | *SW Solver: Extreme grade, overall score 842. | ||

− | *Stephens' estimated times: Improver: N/A, Expert: | + | *Stephens' estimated times: Improver: N/A, Expert: 354 mins, Genius: 118 mins. |

==Solution== | ==Solution== |

## Revision as of 21:04, 15 August 2019

## Contents

## Introduction

- Raw puzzle.
- SW Solver: Extreme grade, overall score 842.
- Stephens' estimated times: Improver: N/A, Expert: 354 mins, Genius: 118 mins.

## Solution

### First pair: Contradiction

See **Figure 1** on the right.
Seed pair is r2c3{38}. Red chain contradiction in c8{9}. Therefore r2c3=3.

(to aid working on the chains, multiple proposed resolutions in a region are marked with lighter versions of the chain colors.)

### Second pair: Contradiction

See **Figure 2** on the left. Seed pair r39c2{2}. Green contradiction, 4s in r8c27. Therefore r8c2=2.

### Third pair: Contradiction

See **Figure 3** on the right. Seed pair r8c7{48}. Contradiction in r4c9, candidates exhausted in red chain. Therefore r8c7=4.

### Fourth Pair: Contradiction and Resolution

See **Figure 4** on the left. Seed pair r1c4{76). Red chain contradiction in r9, two positions for {9}. Therefore r1c4=6. Resolving that, it was singles or easy to full resolution.

## Comments

As might expected, this puzzle required more bifurcations than the previous three of the "Fearsome Five." However, solution time is approximating "Genius" time. It simply takes care, patience and persistence. The alternative, of searching for the truly fearsome number of advanced "logical strategies" needed, many of which actually use similar techniques, will be, except for a true savant, more time-consuming. SBN generates steady progress, almost always. (A very non-productive pair, leading to impasse with no resolutions, only creates progress in terms of identifying a pair not to use, at least from that state!)

SBN may, of course, be combined with advanced strategies. "Impasse" merely means that I did not find a strategy, and I deliberately did not search for non-obvious strategies. If one can find one, it will speed up full resolution. SBN merely makes the other difficult-to-identify advanced strategies unnecessary.