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Nightmare, May 19

 
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ravel



Joined: 21 Apr 2006
Posts: 536
PostPosted: Fri May 19, 2006 11:50 am    Post subject: Nightmare, May 19 Reply with quote
After some UR-puzzles todays nightmare is an experience field for grouped colorings.
2 of them (in 6), a turbot fish and an xy-wing solve the puzzle.
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David Bryant



Joined: 29 Jul 2005
Posts: 559
Location: Denver, Colorado
PostPosted: Fri May 19, 2006 2:20 pm    Post subject: I think it's Nishio Reply with quote
That's interesting, ravel.

I used Nishio on the "6"s and had no other hard moves to make.

I'll explain the Nishio move if you clarify "group coloring" for me. dcb Smile
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ravel



Joined: 21 Apr 2006
Posts: 536
PostPosted: Fri May 19, 2006 3:31 pm    Post subject: Re: I think it's Nishio Reply with quote
David Bryant wrote:

I used Nishio on the "6"s and had no other hard moves to make.

Hm, i checked it with susser and SimpleSudoku now, (after the 6-eliminations) the latter did it the same way as i, susser had complicated moves with standard settings.
But i know, that turbot fish and xy-wing are no hard steps for you.

Quote:

I'll explain the Nishio move if you clarify "group coloring" for me.

I suspect, that you call nishio, what is grouped coloring for me, namely any elimination chain with one number (including the use of x-wing to get a contradiction).
Sample here:
Code:
 *--------------------------------------------------------------------*
 | 489    3      48     | 4679   14679  2      | 5      147    1679   |
 | 7      259    245    | 469    14569  8      | 12469  1234   12369  |
 | 6      259    1      | 3      4579   479    | 249    8      279    |
 |----------------------+----------------------+----------------------|
 | 124    1267   246    | 5      8      4679   | 3      247    1279   |
 | 1245   8      245    | 2479   3      479    | 1249   6      12579  |
 | 3      2567   9      | 2467   2467   1      | 8      2457   257    |
 |----------------------+----------------------+----------------------|
 | 129    4      236    | 269    269    5      | 7      123    8      |
 | 2589   2569   23568  | 1      2679   3679   | 26     235    4      |
 | 125    1256   7      | 8      246    346    | 126    9      12356  |
 *--------------------------------------------------------------------*
r8c2=6 => (r46c2<>6) r4c3=6
r8c2=6 => (r8c67<>6) r9c79=6 => (r9c6<>6) r4c6=6

The reason, that i dont call it nishio is, that many people call it nishio, when they know (from a program), that there is no template (valid setting for a given number in all units) possible for a candidate, but without having a proof.
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David Bryant



Joined: 29 Jul 2005
Posts: 559
Location: Denver, Colorado
PostPosted: Fri May 19, 2006 4:45 pm    Post subject: It's the same thing ... Reply with quote
You're right, ravel -- I did have to use the xy-wing about half-way through this puzzle to eliminate a couple of "4"s. And there was a coloring step that is probably the same thing as the "turbot fish." Please excuse me ... I didn't really get enough sleep last night. Wink

I guess I see why you call it "grouped coloring" ... if I start with a "6" in r9c2 (for instance) and color the cells that are ruled out, I soon learn that r8c7 and r4c3 must also be "6", leaving no way to enter a "6" in column 6. So it looks as if "grouped coloring" and "Nishio" are the same thing ... proving that a certain digit can't go here, because that would make it impossible to enter that digit in all 9 columns, rows, and boxes.

Incidentally, the pattern I actually visualized when I worked this puzzle was an x-wing in r67c45 that made it impossible to place a "6" in box 2 (after placing "6" in r8c2, or r9c2, or r4c3). dcb
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ravel



Joined: 21 Apr 2006
Posts: 536
PostPosted: Sat May 20, 2006 11:47 am    Post subject: Re: It's the same thing ... Reply with quote
David Bryant wrote:

Incidentally, the pattern I actually visualized when I worked this puzzle was an x-wing in r67c45 that made it impossible to place a "6" in box 2 (after placing "6" in r8c2, or r9c2, or r4c3).

Well spotted Smile
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