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Tough Sudoku for 15/March/2010

                 
                 
                 
                 
                 
                 
                 
                 
                 

Choose a number, and place it in the grid above.

  1 2 3 4 5 6 7 8 9
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Sudoku Solving Techniques

Submitted by: sudoku lover

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Opal mines???? I was thinking Fire ant hills!
15/Mar/10 12:37 AM
What a desolate place to find such treasures!
15/Mar/10 3:15 AM
maen all! i've always been fascinated by some of the pictures of homes opal miners have built underground...this looks more like the "digs" we sift for shark's teeth in the venice area of florida!
15/Mar/10 3:27 AM
Hmmm! Interesting. It looks very hot and dry there!
15/Mar/10 3:44 AM
24:45
15/Mar/10 3:52 AM
1. Note pair 29 at g6/i4.Unique possibilities to 25.
2. If c9=4,i1=4.Also c5=4,(triple 567 at b456),b7=8=i9 makes i1=4.UP27.
3. If a6=5,a8=9=c4=i2=d3,g1=2=c2,c3=5,c1=8;bottom middle box is devoid of 8.So a6=9.UP52.
4. If b7=8=i9,f9=6=g8;top left box is devoid of 6.Hence b7=6.UP81.
15/Mar/10 4:41 AM
51 minutes. Rather tough. Or may be I'm rusty?
15/Mar/10 4:51 AM
21:45 ... but, I cheated: when I got stuck at around 12 minutes, it was a lucky guess on one which allowed me to finish.
15/Mar/10 5:10 AM
Thanks for the birthday greetings everyone. Sorry if I missed yours but I cannot acess Sudoku in college.
15/Mar/10 8:06 AM
41:24
15/Mar/10 11:25 AM
Hello Jyrki, nice to see you back!

We are going to stay in an underground motel, in August at White Cliffs, on our Broken Hill trek. Should be interesting, and there is a tour of the opal mines.
15/Mar/10 2:40 PM
1. Given UP=23. b2=1, g7=7, pairs 29 at g6/i4, locked 3s at a89/ef7, UP=25.
2. 9 can be at c7 or f7. If f7=9, e7=3, a8=9, a9=3, pairs 39 at c45, c5=3=d4, c4=9=g6=i2 which leaves d2 blank. So f7<>9 but c7=9. UP=26. Follow: UPs at a6, i4, g3, g6. UP=30.
3. 4 can be at i1 or i9. If i9=4, More...
15/Mar/10 3:58 PM
1) Basic techniques to UP=25.
2) (4)e3=(4-9)g3=(9)i2-(9=2)i4-(2=4)i1=>e1g3<>4. UP=26.
3) (2=59)i2-(5=3679)defh2-(9=25)i2=>i2<>9. UP=31.
4) (4)c9=(4)c5-(4=567)b456-(56=8)b7-(8)i7=(8)i9=>i9<>4, UP=52.
5) (6=8)b7-(8=46)bg8=>a8<>6, UP=81.
15/Mar/10 6:46 PM
Typo in the last line of my proof: the correct wording should be '......no 4 in column b' (instead of 'column 2'). Sorry for the error.
Thanks to Alfred from Sydney for pointing this out.
15/Mar/10 7:18 PM
One more typo in my proof. In step 3, it should read '..leaving no 8 in column b..', instead of '..leaving no 8 in column i..'.
15/Mar/10 11:29 PM

1)Start at 22,basic techniques to UP=25
2)ALS:(4=35698)a89b7c79-(8)i7=(8)i9,=>i9<>4.UP=27
3)YWS:((9=5)g3-ac3=(5-2)c2=(2)i2, =>i2<>9.UP=52
4)YWS:(5=6)a8-(6=4)g8-g9=(4)c9,=>c9<>5.UP=81
16/Mar/10 1:52 AM

Hi Neil,
Step 2 doesn't work,first you have to eliminate h3=4:
(4)h6=b6-c5=c9-i9=i1,=>h13<>4.
Step 2 better should be:
ALS:(5=3679)defh2-(9)d3=(9)g3,=>g3<>5
Step 5 is OK.=>Step 2 is not necessary.
So, 1)=>UP=25
2)=>i9<>4.UP=27
3)=>g3<>5 .UP=52
4)=>a8<>6.UP=81
Regards,Sotir

16/Mar/10 2:54 AM

SE=8.2
10/Sep/10 9:03 PM
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