The New Sudoku Players' Forum

[JEAGoodman]

Ok, so I thought I was starting to get "Exclude based on Colors" until I saw this one.

Why on earth are all of the blue colors for 5 excluded? (R4C1, R5C4, R7C1, R9C6)

*-----------------------------------------------------------*
| 9 5 47 | 46 1 8 | 246 3 2467 |
| 4678 2 478 | 3 9 467 | 468 1 5 |
| 4678 3 1 | 2 5 467 | 9 478 467 |
|-------------------+-------------------+-------------------|
| 58 89 6 | 7 4 59 | 3 2 1 |
| 345 49 345 | 589 2 1 | 68 78 679 |
| 1 7 2 | 89 6 3 | 5 48 49 |
|-------------------+-------------------+-------------------|
| 345 1 9 | 45 8 2 | 7 6 34 |
| 2348 468 348 | 469 7 469 | 1 5 234 |
| 2457 46 457 | 1 3 456 | 24 9 8 |
*-----------------------------------------------------------*

Jeanne

[re'born]

JEAGoodman,

Remember that when you color, two squares that are colored the same will always have the same truth value. That is to say, if two squares are colored blue (say we are coloring 5's), then they will either both be 5 or both not be a 5. In your example, cells (4,1) and (7,1) are both colored blue. If they were both 5, then there would be two 5's in column 1, a contradiction. Therefore they (along with any other blue) must not be a 5.

[JEAGoodman]

Thank you, thank you, thank you! That makes perfect sense! I was getting sore from banging my head against the wall.

Jeanne