## Something about coloring that I don't understand

Post the puzzle or solving technique that's causing you trouble and someone will help

### Something about coloring that I don't understand

I took some puzzle to this stage:
Code: Select all
`.-------------.-------------.---------------.| 19  3   179 | 4    6  5   | 8     12  127 || 5   2   17  | 38   9  38  | 17    6   4   || 4   8   6   | 7    2  1   | 5     9   3   |:-------------+-------------+---------------:| 2   19  5   | 19   4  7   | 3     8   6   || 8   4   19  | 36   5  36  | 1279  12  127 || 7   6   3   | 19   8  2   | 19    4   5   |:-------------+-------------+---------------:| 6   19  2   | 5    7  49  | 14    3   8   || 3   5   8   | 26   1  46  | 246   7   9   || 19  7   4   | 268  3  689 | 126   5   12  |'-------------'-------------'---------------'`

Since there were several (1,9) couples I thought there would be good chaces of elimination using coloring while filtering on 1's, so I marked (with opposite colors depending on their location of course) r7c2, r9c1, r1c1, r4c2, r5c3, r4c4 and r6c7.

Now since r5c3 and r6c7 both have the same color, I thought all cells seen by both (r5c789), could have their 1's removed, but that is wrong.

Could someone please clarify what I am understanding wrong here.
Thanks
JeJ

Posts: 76
Joined: 06 January 2011

### Re: Something about coloring that I don't understand

JeJ wrote:Now since r5c3 and r6c7 both have the same color, I thought all cells seen by both (r5c789), could have their 1's removed, but that is wrong.

A validly eliminated candidate must see both of the "opposing" colors. Why? We know one of the two colors must ultimately be true.
Last edited by ronk on Thu Mar 10, 2011 4:27 pm, edited 1 time in total.
ronk
2012 Supporter

Posts: 4764
Joined: 02 November 2005
Location: Southeastern USA

### Re: Something about coloring that I don't understand

JeJ wrote:Now since r5c3 and r6c7 both have the same color, I thought all cells seen by both (r5c789), could have their 1's removed, but that is wrong.

Could someone please clarify what I am understanding wrong here.
Thanks

Basic Coloring (type 1) forces eliminations in cells that see both colors; i.e., r9c7.

Coloring (type 3) was mentioned by Angus Johnson and recently discussed somewhere (that I forgot). Anyway, your puzzle has a perfect example of it. Your cells r5c3 and r6c7 are the same color, and they see the only two cells in [row 2] that contain <1>. Any cells with the color of r5c3 and r6c7 can't be true for <1>!!!
daj95376
2014 Supporter

Posts: 2624
Joined: 15 May 2006

### Re: Something about coloring that I don't understand

Duh! I was really wrong on this.

Thanks for the clarification.
JeJ

Posts: 76
Joined: 06 January 2011