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From websudoku.com

Given:
...|3.1|...
...|...|3.7
.45|.8.|..6
-----------
89.|..4|...
.21|.3.|47.
...|8..|.61
-----------
1..|.7.|53.
2.9|...|...
...|2.3|...

got as far as:
..2|3.1|8.5
.18|...|3.7
345|.8.|1.6
-----------
89.|..4|253
.21|.3.|478
4.3|8..|961
-----------
1..|.7.|532
239|...|7.4
...|2.3|6.9

At this point I got stuck. According to Angus J's Simple Sudoku program candidate no.9 can be eliminated from these cells:
(4,2) (6,2) (4,3) (6,3) using (Column, Roll) notation.

From this point on I can solve it, but I do not understand the principle of the deduction here. If it makes sense to you kindly advise, thanks!
apatt

Posts: 26
Joined: 28 July 2005

apatt wrote:I do not understand the principle of the deduction here.

http://angusj.com/sudoku/hints.php#locked_candidates_2
angusj

Posts: 306
Joined: 12 June 2005

It's a little confusing at first I know - but it's saying - 'column 1 has got to have a 9 in it - and the only block that has 9's in column 1 is the middle block - so column 1 of the middle block is supplying not only the COLUMN with a 9, but the BLOCK with a 9. Therefore we can remove 9 as a candidate from the other cells in the block' -

but that aside, you've already got a big 9 at r4c2 ! - maybe an input was dodgy.

Last edited by stuartn on Fri Aug 12, 2005 5:12 am, edited 1 time in total.
stuartn

Posts: 211
Joined: 18 June 2005

now i'm confused, thought we look at column 5.
Wolfgang

Posts: 208
Joined: 22 June 2005

Hi, try something like this:
look at your 3s (for instance); the top band of blocks holds two 3s. Only one other three can appear in any of those rows. What about the missing 3 in the right, top block? Which row could it appear in?

Using the 3s you have already will help you find all your 3s, remembering that each 3 you see is the only 3 that is allowed to appear in that block, in that row AND in that column.
LittleBird

Posts: 3
Joined: 11 August 2005

Hello apatt!

Look at row 5 and row 7. For both those rowa, 9 can only be in either column 4 or column 6. So then one of them has to have it in column 4 and the other in column 6. Therefore, the 9 can NOT be in column 4 and column 6 for any other row than 5 and 7. So you can remove 9 as a candidate for row 2 and row 3 for column 4 an d 6.

/Anette
Anette

Posts: 55
Joined: 09 June 2005

apatt wrote:According to Angus J's Simple Sudoku program candidate no.9 can be eliminated from these cells:
(4,2) (6,2) (4,3) (6,3) using (Column, Roll) notation.

From this point on I can solve it, but I do not understand the principle of the deduction here. If it makes sense to you kindly advise, thanks!

You probably already figured it out based from Angusj's reply, but the other posts may re-confuse you. It might help to look here for the terms and notation in common usage.

The deduction that the program used to remove those four candidates was: Column 5 has exactly two cells with candidate 9's -- in row 1 and 2. One of these MUST be a 9 -- therefore, no other 9's can be in box 2.

Wolfgang is not alone; I cannot figure out what Stuartn's post means.

Anette is pointing out another perfectly good deduction that could have been used at the same point to eliminate the same four candidate 9's -- an 'x-wing' in the four cells at row 5 and 7, columns 4 and 6. Simple Sudoku considers this a more advanced tactic then 'possibles locked in a column', but in this case, it has exactly the same results, and is 35-40% more fun to spot.
tso

Posts: 798
Joined: 22 June 2005

Hi!

Thanks for all the replies, especially Tso's for the notation tip!
(I meant to type "row", not "roll", sorry, must have been thinking of something else)
apatt

Posts: 26
Joined: 28 July 2005