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George Woods
Joined: 28 Mar 2006
Posts: 304
Location: Dorset UK
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 Posted: Tue Jan 27, 2015 2:41 pm Post subject: Can anyone help identify my solution;s typr? |
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| Code: |
+-------------+------------+----------------+
| 1 4 7 | 6 89 3 | 5 289 289 |
| 9 2 3 | 145 48 15 | 7 6 48 |
| 8 5 6 | 47 2 79 | 49 3 1 |
+-------------+------------+----------------+
| 4 6 29 | 3 7 8 | 129 129 5 |
| 27 3 1 | 9 5 4 | 6 278 28 |
| 5 79 8 | 2 1 6 | 49 479 3 |
+-------------+------------+----------------+
| 3 19 249 | 145 6 159 | 8 1249 7 |
| 267 8 249 | 147 3 179 | 1249 5 2469 |
| 67 179 5 | 8 49 2 | 3 149 469 |
+-------------+------------+----------------+
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Play this puzzle online at the Daily Sudoku site
This is as far as I get with "conventional' techniques with the Brainbashers Jan 26 Superhard (and incidentally DS draw/play agrees)
My solution is to note that there are two positins for 7 in box 6 and whichever is chosen we get r3c7 =9 and that solves the puzzle - So what family does this logic belong to? |
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Marty R.
Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA
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| Posted: Tue Jan 27, 2015 4:54 pm Post subject: Re: Can anyone help identify my solution;s typr? |
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| George Woods wrote: | | Code: |
+-------------+------------+----------------+
| 1 4 7 | 6 89 3 | 5 289 289 |
| 9 2 3 | 145 48 15 | 7 6 48 |
| 8 5 6 | 47 2 79 | 49 3 1 |
+-------------+------------+----------------+
| 4 6 29 | 3 7 8 | 129 129 5 |
| 27 3 1 | 9 5 4 | 6 278 28 |
| 5 79 8 | 2 1 6 | 49 479 3 |
+-------------+------------+----------------+
| 3 19 249 | 145 6 159 | 8 1249 7 |
| 267 8 249 | 147 3 179 | 1249 5 2469 |
| 67 179 5 | 8 49 2 | 3 149 469 |
+-------------+------------+----------------+
|
Play this puzzle online at the Daily Sudoku site
This is as far as I get with "conventional' techniques with the Brainbashers Jan 26 Superhard (and incidentally DS draw/play agrees)
There is a naked pair (49) in c7, but I don't know if it's of any significance.
My solution is to note that there are two positins for 7 in box 6 and whichever is chosen we get r3c7 =9 and that solves the puzzle - So what family does this logic belong to? |
It looks to me like a Forcing Chain, which some view as trial and error. There is a potential UR on 28 in boxes 36. Either r1c89=9 or r5c8=7. That's the move I would try if I tried to finish this puzzle. |
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George Woods
Joined: 28 Mar 2006
Posts: 304
Location: Dorset UK
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| Posted: Tue Jan 27, 2015 5:07 pm Post subject: forcing chain? trial and error |
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| It was the potential Ur in 28 that set me thinking about the 7s in box 6 and putting the 7 such that the UR was potentially there as well as in a place that saves the UR which lead me to my solution. It is very like a wing what with one of two 4s bearing down on the 49 at r3c7 depending on the toggle of the 7s |
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dongrave
Joined: 06 Mar 2014
Posts: 572
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| Posted: Wed Jan 28, 2015 1:43 am Post subject: |
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Hi George, I call your type of solution a 'Van Hay' solution because he was the first one I saw do it but from what I remember from logic class all those years ago, I'm sure that De Morgan knew it a LONG time before Van Hay did! A or B; A implies C; B implies C; therefore C.
A while ago, I sent the exact same question and asked specifically for someone to show me how to represent it in Eureka notation (which I despised at the time). Marty showed me how it really was the same thing as a forcing chain by beginning with the assumption of the wrong value and then combining the 2 different chains to show the contradiction. Interesting stuff! (at least to me.)
By the way, in your grid, the 48 naked pair in row 2 eliminates the 4 from r2c4 which creates a UR (Type 3) of 15's in r27c46 so r8c4<>4 and r8c6<>9 (because r9c5 is 4 or 9) creating a 17 naked pair in row 8 which also solves it - but I don't think this solution is any better than yours.
I also noticed that there are a few more basic eliminations missing from your grid but they don't look very important (at least at first glance). There's also a 49 naked pair in column 7 that removes them from the other rows and there are restricted 7's in box 8 that removes it from r8c1. |
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arkietech
Joined: 31 Jul 2008
Posts: 1834
Location: Northwest Arkansas USA
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| Posted: Wed Jan 28, 2015 2:00 pm Post subject: |
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Skyscraper in c17 solves it  |
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