8.9 from Reddit 2025-05-13

 Someone on the r/Sudoku Reddit posted this puzzle innocently asking for help:

Original Post

..9.3.56.........7.5.....8957......4..8..2....3..6.1...8.4........6...3..1.3.59.. - Sudoku.Coach

SE 8.9

Let's get started.

Sashimi X-Wing

Kraken Column: (2)r8c2 = [(2=7)r7c7 - (7=6)r5c7 - r5c2 = (6-2)r2c2 = r1c2 - (2=1)r1c9 - r2c8 = r7c8 - (1=792)r7c567] => r7c13<>2

(1=9)r4c5 - r456c4 = (9-5)r2c4 = (5)r2c5 => r2c5<>1

(8)r6c9 = (8-6)r4c7 = (6-2)r4c3 = (2)r6c13 => r6c9<>2

(4)r9c8 = (4-1)r2c8 = (1-2)r1c9 = (2)r789c9 => r9c8<>2

ALS-XZ: (4=7)r9c8 - (7=234)r237c7 => r2c8, r8c7<>4

Naked Pair

(1=2)r2c8 - (2=9)r4c8 - (9=1)r4c5 - r4c3 = (1)r5c1 => r2c1<>1

Kraken Column: (2)r8c2 = [(2=7)r7c7 - (7=6)r5c7 - r5c2 = (6-2)r2c2 = r1c2 - r1c9 = (2)r789c9] => r8c7<>2

(7=8)r8c7 - r9c9 = (8-7)r9c5 = (7)r9c13 => r8c13<>7

(6)r4c3 = r4c7 - (6=7)r5c7 - (7=286)b9p149 => r9c3<>6

(1)r123c4 = r45c4 - (1=9)r4c5 - (9=2)r4c8 - (2=1)r2c8 => r2c6<>1

(356)(r7c139 = r7c8) - (1)r7c8 = (1-2)r2c8 = (2)r1c9 => r7c9<>2

(4=2)r1c2 - r1c9 = r89c9 - (2=7)r7c7 - (7=6)r5c7 - r5c2 = (6)r2c2 => r2c2<>4

Kraken Column: (7=2)r9c3 - (2)r8c2 = [(7=2)r7c7 - r89c9 = r1c9 - r1c2 = (2-6)r2c2 = r6c2 - (6=7)r5c7 - r56c8 = (7)r7c8] => r7c13<>7

Kraken Column: (6)r5c2 = (6-2)r2c2 = [(6=72)r9c13 - r8c2 = r1c2 - r1c9 = r89c9 - (2=76)r57c7] => r5c1<>6

Getting a lot of use from this 2c2 Kraken link :D

AIC-tie-AIC: [(4=2)r1c2 - r1c9 = r2c8 - (2=9)r4c8 - (9=1)r4c5 - (1=4)r3c5] = (7)r3c5 - (7)r1c4 = [(4=2)r1c2 - (2=18)r1c49 - (8=19)r4c45 - (9=2)r4c8 - r2c8 = r1c9 - (2=4)r1c2] => r1c6, r3c13<>4

These two almost-AIC are weakly linked by 7b2 so both cannot be false at once.

(8)r9c5 = r9c9 - (8=5)r6c9 - r8c9 = (5-4)r8c3 = r6c3 - r5c12 = (4-5)r5c5 = (5)r2c5 => r2c5<>8

AHS-XZ: (59)(r2c4 = r2c56) - (468)(r2c6 = r136c6) => r2c4<>8

(1=9)r4c5 - (9=2)r4c8 - r4c7 = r7c7 = (28)(r7c5 = r89c5) => r8c5<>1

(8)r2c1 = (8)r2c6 - (46)(r2c6 = r36c6) - (4)r6c3 = (4-5)r8c3 = r8c9 - r7c89 = (5-3)r7c3 = (3)r7c1 => r2c1<>3

(1)r8c6 = (1-5)r8c9 = (5-4)r8c3 = r6c3 - (46)(r6c6 = r23c6) => r3c6<>1

Kraken Row: (7)r8c6 = [(7)r8c7 = (7)r8c5 - (28)(r8c5 = r79c5) - (2=7)r7c7] - (7=6)r5c7 - r5c2 = r2c2 - r2c6 = (6)r3c6 => r3c6<>7

AHS-AIC: (28)(r8c5 = r79c5) - (2)r7c7 = r4c7 - (12)(r46c8 = r27c8) - (356)(r7c8 = r7c139) - (9)r7c1 = (9)r7c56) => r8c5<>9

Kraken X-Wing: (8)r2c1 = (8)r2c6 - (46)(r2c6 = r36c6) - (4)r5c5 = r15\c12 - (4=92)r68c1 => r2c1<>2

(8)r2c1 = r2c6 - (46)(r2c6 = r36c6) - (4)r6c3 = (4-5)r8c3 = (5-6)r7c3 = (6)r79c1 => r2c1<>6

(9=64)r23c6 - (45)(r3c5 = r25c5) => r2c5<>9

(9)r7c5 = r78c6 - (9=64)r23c6 - r6c6 = (4)r5c5 => r5c5<>9

(2)r7c7 = r4c7 - (2=9)r4c8 - r4c5 = (9)r7c5 => r7c5<>2

Naked Triple

(5=8)r6c9 - r4c7 = (8-7)r8c7 = (7-1)r8c6 = (1)r8c9 => r8c9<>5

Triple

W-Wing

(7)r7c5 = r3c5 - r3c3 = (7-2)r9c3 = (2-9)r8c2 = (9)r8c6 => r7c5<>9, r8c6<>7

STTE