Interesting SK loop

Advanced methods and approaches for solving Sudoku puzzles

Interesting SK loop

Postby pjb » Wed Jun 27, 2018 8:08 am

I came across the following puzzle in the Patterns game posted by Dobrichev on May 19, 2018:

.123.....45.......3.6...7..6..7..4......2...8.....5.9...46..3.......9.5.....8...2

It has an SK loop (or whatever you prefer to call them) of the classic type:

(13=89)r4c56 - (89=14)r56c4 - (14=25)r89c4 - (25=17)r7c56 - (17=89)r7c89 - (89=16)r89c7 - (16=25)r56c7 - (25=13)r4c89 - loop
r4c2 <> 3; r4c3 <> 1; r4c3 <> 3; r7c1 <> 1; r7c1 <> 7; r7c2 <> 7; r2c4 <> 1; r3c4 <> 1; r3c4 <> 4; r1c7 <> 6; r2c7 <> 1; r2c7 <> 6;

However to my surprise it also has in the same cells a loop of the variant kind (one digit link between boxes and 3 within boxes):

(3=189)r4c56 - (189=4)r56c4 - (4=125)r89c4 - (125=7)r7c56 - (7=189)r7c89 - (189=6)r89c7 - (6=125)r56c7 - (125=3)r4c89 - loop
r4c2 <> 3; r4c3 <> 3; r7c1 <> 7; r7c2 <> 7; r3c4 <> 4; r1c7 <> 6; r2c7 <> 6; r5c6 <> 1; r6c5 <> 1; r5c8 <> 1; r6c9 <> 1; r8c5 <> 1; r9c6 <> 1; r8c9 <> 1; r9c8 <> 1

Phil
pjb
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Re: Interesting SK loop

Postby Leren » Wed Jun 27, 2018 10:36 am

Hi Phil, also found a Multifish : Truths 18 Base 2589 Rows 12347; Links 18 Cols 5689 Box 1 Cells r1c7 r2c4 r2c7 r3c4 r4c2 r4c3 r7c1 r7c2 which gives the same 12 eliminations as the SK loop.

Also, if I play the SK loop first I get a second Multifish : Truths 20 Base 12589 Rows 4 & 7 Cols 4 & 7; Links 20 Boxes 5, 6, 8 & 9 Cells r2c4 r3c4 r4c2 r4c3 r1c7 r2c7 r7c1 r7c2 => - 1 r59c68, r68c59.

Intriguingly all the SK loop eliminations occur in the pivot loop cells with none in the boxes. Can't say I've ever seen that behaviour before, but then I haven't played an SK loop for years.

Leren
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Re: Interesting SK loop

Postby champagne » Thu Jun 28, 2018 5:54 am

Leren wrote:Hi Phil, also found a Multifish : Truths 18 Base 2589 Rows 12347; Links 18 Cols 5689 Box 1 Cells r1c7 r2c4 r2c7 r3c4 r4c2 r4c3 r7c1 r7c2 which gives the same 12 eliminations as the SK loop.

Also, if I play the SK loop first I get a second Multifish : Truths 20 Base 12589 Rows 4 & 7 Cols 4 & 7; Links 20 Boxes 5, 6, 8 & 9 Cells r2c4 r3c4 r4c2 r4c3 r1c7 r2c7 r7c1 r7c2 => - 1 r59c68, r68c59.

Intriguingly all the SK loop eliminations occur in the pivot loop cells with none in the boxes. Can't say I've ever seen that behaviour before, but then I haven't played an SK loop for years.

Leren

Hi both,

A skloop has always several corresponding multi fish , the shortest is done of the 16 cells as sets. Normally, if a pattern is "SKloop compatible " many high ratings will have a SK loop. This is often true when the number of clues is small.
champagne
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