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Sudoku - Extra Diabolical — Solution #1

Difficulty: EXPERT Clues: 27 Hardest: BACKTRACKING 65 steps
0 / 65
NAKED SINGLE #1 R1C6 = 4 (only candidate)
NAKED SINGLE #2 R8C5 = 8 (only candidate)
NAKED SINGLE #3 R1C5 = 6 (only candidate)
HIDDEN SINGLE #4 R1C1 = 3 (only place for 3 in Row 1)
HIDDEN SINGLE #5 R2C7 = 4 (only place for 4 in Row 2)
HIDDEN SINGLE #6 R3C8 = 3 (only place for 3 in Row 3)
HIDDEN SINGLE #7 R3C2 = 6 (only place for 6 in Row 3)
HIDDEN SINGLE #8 R5C3 = 3 (only place for 3 in Row 5)
HIDDEN SINGLE #9 R8C4 = 3 (only place for 3 in Row 8)
HIDDEN SINGLE #10 R7C4 = 5 (only place for 5 in Col 4)
HIDDEN SINGLE #11 R8C1 = 9 (only place for 9 in Box 7)
NAKED SINGLE #12 R8C9 = 1 (only candidate)
NAKED SINGLE #13 R1C9 = 8 (only candidate)
NAKED SINGLE #14 R8C3 = 5 (only candidate)
LOCKED CANDIDATES POINTING #15 1 in Box 3 → Col 7; eliminate from 2 cell(s)
LOCKED CANDIDATES POINTING #16 7 in Box 5 → Row 5; eliminate from 4 cell(s)
HIDDEN SINGLE #17 R6C1 = 7 (only place for 7 in Col 1)
LOCKED CANDIDATES POINTING #18 8 in Box 9 → Col 8; eliminate from 2 cell(s)
XY WING #19 Pivot R2C1{5,8}, pincers R1C2 & R9C1; eliminate 1 from 1 cell(s)
SIMPLE COLORING #20 Coloring (trap): 1 — cell(s) see both colors; eliminate from 1 cell(s)
LOCKED CANDIDATES POINTING #21 1 in Box 5 → Col 4; eliminate from 1 cell(s)
SIMPLE COLORING #22 Coloring (trap): 4 — cell(s) see both colors; eliminate from 1 cell(s)
BACKTRACKING #23 Try R1C2 = 1 (trial and error)
NAKED SINGLE #24 R1C7 = 5 (only candidate)
NAKED SINGLE #25 R2C8 = 9 (only candidate)
NAKED SINGLE #26 R3C9 = 7 (only candidate)
NAKED SINGLE #27 R3C7 = 1 (only candidate)
NAKED SINGLE #28 R5C7 = 8 (only candidate)
NAKED SINGLE #29 R4C7 = 7 (only candidate)
NAKED SINGLE #30 R4C8 = 1 (only candidate)
NAKED SINGLE #31 R7C9 = 9 (only candidate)
HIDDEN PAIR #32 {1,6} confined to R5C4 & R6C4; eliminate 3 candidate(s)
NAKED TRIPLE #33 R5C1, R5C4, R5C8 share {1,5,6}; eliminate from 1 cell(s)
XY WING #34 Pivot R9C4{2,4}, pincers R2C4 & R9C2; eliminate 8 from 1 cell(s)
SIMPLE COLORING #35 Coloring (trap): 4 — cell(s) see both colors; eliminate from 2 cell(s)
NAKED SINGLE #36 R4C3 = 8 (only candidate)
NAKED SINGLE #37 R3C3 = 2 (only candidate)
NAKED SINGLE #38 R2C2 = 5 (only candidate)
NAKED SINGLE #39 R2C1 = 8 (only candidate)
NAKED SINGLE #40 R2C4 = 2 (only candidate)
NAKED SINGLE #41 R3C6 = 9 (only candidate)
NAKED SINGLE #42 R3C4 = 8 (only candidate)
NAKED SINGLE #43 R5C6 = 7 (only candidate)
NAKED SINGLE #44 R5C5 = 4 (only candidate)
NAKED SINGLE #45 R4C4 = 9 (only candidate)
NAKED SINGLE #46 R4C2 = 4 (only candidate)
NAKED SINGLE #47 R5C9 = 2 (only candidate)
NAKED SINGLE #48 R5C2 = 9 (only candidate)
NAKED SINGLE #49 R6C2 = 2 (only candidate)
NAKED SINGLE #50 R6C3 = 1 (only candidate)
NAKED SINGLE #51 R5C1 = 5 (only candidate)
NAKED SINGLE #52 R5C8 = 6 (only candidate)
NAKED SINGLE #53 R5C4 = 1 (only candidate)
NAKED SINGLE #54 R6C4 = 6 (only candidate)
NAKED SINGLE #55 R6C8 = 5 (only candidate)
NAKED SINGLE #56 R6C9 = 4 (only candidate)
NAKED SINGLE #57 R7C3 = 4 (only candidate)
NAKED SINGLE #58 R7C5 = 7 (only candidate)
NAKED SINGLE #59 R7C6 = 1 (only candidate)
NAKED SINGLE #60 R7C8 = 8 (only candidate)
NAKED SINGLE #61 R9C1 = 1 (only candidate)
NAKED SINGLE #62 R9C2 = 8 (only candidate)
NAKED SINGLE #63 R9C4 = 4 (only candidate)
NAKED SINGLE #64 R9C6 = 2 (only candidate)
NAKED SINGLE #65 R9C8 = 7 (only candidate)