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Tough Sudoku for 19/May/2015

                 
                 
                 
                 
                 
                 
                 
                 
                 

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

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Sudoku Solving Techniques

Submitted by: sudoku lover

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Standard techniques UP 34
1. (6=7)a9-(7=3)e9-e7=(3)b7 =>-6b7 UP 81
19/May/15 1:04 AM
Handsome critter!
19/May/15 1:14 AM
Hi cenoman.I could'nt quite follow your solution today, probably because I only got to UP33 for step 1.
1. Note a19=67,a23=19.Unique possibilities to 33.
2. Whether h2=7=a1;OR hca7=578,e9=7;a9=6.UP81.
19/May/15 1:50 AM
Hi Alfred,
I guess you are missing the SIS 3b7=3e7 in my chain, because of the candidate 3 in i7.
My last unique possibility is d1=4.
Once you get 33 solved cells, you can note the locked 4 at i79 =>-4i13, then you get i1.h23=679, consequently the 9 are locked at h23=>-9h78 and therefore fi7=49 (eliminating 3 from i7, q.e.d.)
Best regards. cenoman.
19/May/15 3:30 AM
I like goatees. Doesn't matter if they're on goats or guys!
19/May/15 6:56 AM
Thanks cenoman. I missed d1=4, and I don't know if I would have noticed fi1=49 after that either.
However, after you show b7<>6, can't b8 still become 6, (not only a9)?
Best Regards, Alfred.
19/May/15 7:56 AM
Hi Alfred,
b7<>6 then h7=6, then i1=6 =>a1=7 and therefore a9=6
Best regards, cenoman.
19/May/15 8:36 AM
Thanks again cenoman. It's all clear now.
19/May/15 9:55 AM
#29 4@i79=>i1<>4 #30 357@f8<>5 #31 3@b78=>67@a19=>58@a57=>a46<>568&a7<>6 #34 67@a19=>58@a5c6=>c4<>58
#35 679@h23i9=>g23i3<>69 49@fi7=>fi7<>6 3?@b7=>[h7=6=>i1=6&e7=7=>c2=7]=>a1={}=>b7<>3
#36 More...
19/May/15 10:34 AM
Another route:
UP 33 c3 = (7,8)
if c3 = 7, e7 = 7
if c3 = 8, c7 = 7,h7<>7
if c3 = 7,h7=8
exception as ac7=(5,8)
UP81
19/May/15 1:16 PM
That would be the most straightforward 'Tough' ever. I had to keep checking to make sure I wasn't doing a 'Medium'.
19/May/15 5:33 PM
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